To date several observational studies have been conducted and these studies consistently show real-world effectiveness of homeopathic treatment. Although one cannot attribute causality to interventions studied using this type of design, these studies can make a valuable contribution to essential developmental research in homeopathy and suggest areas where it might be effective. They may even have several advantages over randomized controlled trials, including lower cost, greater timeliness, and a broader range of patients.

Papers in respected conventional medical journals such as the New England Journal of Medicine, have shown that well-designed cohort or case-controlled observational studies do not overestimate treatment effect sizes.
Benson K, Hartz AJ (2000). A comparison of observational studies and randomized, controlled trials. New England Journal of Medicine, 342:1878-1886 [PubMed]

Concato J, Shah N, Horwitz RI (2000).Randomized, controlled trials, observational studies, and the hierarchy of research designs. New England Journal of Medicine, 342:1887-1892 [PubMed]

Several good-quality observational studies in single medical conditions suggest that homeopathy may be useful in averting the need for other, undesirable treatment, such as antibiotics for acute otitis media and methylphenidate (Ritalin) for ADHD. In 230 children with acute otitis media treated with homeopathy, 72% were pain-free within 12 hours, a resolution rate that is 2.4 times faster than reported in other series. No complications were observed, and there are potential cost savings. In a study of similar design, but in a less acute situation, 115 children with ADHD received an individual homeopathic treatment. After an average treatment time of 3.5 months, 75% of the children had responded sufficiently not to require methylphenidate, with a mean clinical improvement rating of 73%.
Frei H, Thurneysen A (2001). Homeopathy in acute otitis media in children: treatment effect or spontaneous resolution? Homeopathy, 90:180–182 [PubMed]
Frei H, Thurneysen A (2001). Treatment for hyperactive children: homeopathy and methylphenidate compared in a family setting. Homeopathy, 90:183–188 

A prospective documentation study sponsored by a German health insurance company examined the effects of acupuncture and homeopathy in terms of quality of life, doctors’ rating of change and work absenteeism. Over 900 patients were treated with homeopathy; most had chronic complaints. Treatment had ‘middle to large-sized’ effects on patient-assessed quality of life, and there were highly significant reductions in work absenteeism.
Güthlin C, Lange O, Walach H (2004). Measuring the effects of acupuncture and homoeopathy in general practice: An uncontrolled prospective documentation approach. BMC Public Health, 4:6[PubMed]

A prospective, multi-centre cohort study included 103 primary care / homeopathy practices in Germany and Switzerland. Data from all patients (age > 1 year) consulting the physician for the first time were recorded: 2,851 adults and 1,130 children. The main outcome measures were patient and physician assessments and quality of life at baseline, and after 3, 12, and 24 months. Ninety-seven percent of all diagnoses were chronic (average duration 8.8 years). 95% of patients had received conventional treatment prior to the start of the study. Disease severity decreased significantly (P < 0.001) between baseline and 24 months. For adults and young children, major improvements were observed for quality of life, whereas no changes were seen in adolescents. Disease severity and quality of life demonstrated marked and sustained improvements following homeopathic treatment.
Witt CM, Lüdtke R, Baur R, Willich SN (2005). Homeopathic medical practice: long-term results of a cohort study with 3,981 patiënts. BMC Public Health, 5:115 [PubMed]

An observational study at a public sector homeopathic hospital in the UK included over 6,500 consecutive patients with over 23,000 attendances in a 6-year period. 70% of follow-up patients reported improved health, 50% major improvement. The most common diagnostic groups were Dermatology, Neurology, Rheumatology, Gastroenterology, Psychiatry and Ear, Nose & Throat. The best treatment responses were reported in childhood eczema or asthma, and in inflammatory bowel disease, irritable bowel syndrome, menopausal problems and migraine. The main weakness of this study (apart from those inherent to non-controlled designs) is the crudeness of the outcome measure; the strength of the work is in its size and comprehensiveness.
Spence D, Thompson EA, Barron SJ (2005). Homeopathic treatment for chronic disease: a 6-year university-hospital outpatiënt observational study. Journal of Alternative and Complementary Medicine, 5:793–798 [PubMed]

A 500-patient survey at another UK public sector homeopathic hospital showed that many patients were able to reduce or stop conventional medication following homeopathic treatment. The size of the effect varied between diagnoses: for skin complaints, for example, 72% of patients reported being able to stop or reduce their conventional medication, but for cancer patients there was no reduction. The study also showed that many patients seek homeopathy because of their concerns about the safety of conventional treatment.
Sharples F, van Haselen R, Fisher P (2003).  NHS patiënts’ perspective on complementary medicine.  Complementary Therapies in Medicine, 11:243–248 [PubMed]