Objective-To ascertain the incidence and prevalence of juvenile arthritis in a German urban population. Methods-All 766 paediatricians, orthopaedists, and rheumatologists working in practices or outpatient clinics in 12 south German towns were asked to report all patients who consulted them for juvenile arthritis during the year 1995. Patients with continuing symptoms were followed up for 9-12 months to obtain a final diagnosis. Extended measures of quality control were taken to control for known biases. Results-Of 457 reported cases, 294 were diagnosed with para-/postinfectious arthritis (PPA), 78 with juvenile chronic arthritis (ICA), and IS with other forms of arthritis. Half of the PPA cases were classified as transient synovitis of the hip (SH). For JCA the reported annual incidence was 6.6 and the prevalence 14.8 per 100 000 subjects under 16 years of age. For PPA the reported incidence was 76 and the prevalence 4.4 per 100 000 subjects under 16. The incidence of rheumatic fever was clearly below 1 per 100 000 people under 16. A correction model was used to control for known biases and to adjust the estimates accordingly. Conclusions-The results of this first prospective study on the incidence and prevalence of juvenile arthritis in Germany are consistent with a retrospective study performed in the Berlin area. Based on these results it was estimated that the annual frequency of juvenile arthritis in Germany is as follows: 750-900 incident JCA cases, 21 000 incident SH cases, and 21 000 incidence cases of other forms of PPA a year. The number of incidence cases of rheumatic fever is expected to be markedly lower than 150 a year. The total prevalence is expected to be 3600-4350 JCA cases, 2250-3000 SH cases, and the same number of other forms of PPA.