We evaluated the natural long-term outcome after childhood IgA nephritis. Altogether 55 patients with biopsy-proven IgA nephritis were identified, 37 (67%) responded to the health questionnaire and 31 (56%) participated in the medical examination after a mean follow-up of 18.7 years (SD 6.2; range 8.5-29.8). The results of medical examination, onset data and the re-analysis of original biopsies of 31 participants were used when analyzing the predictive factors for persistent nephropathy, i.e. constant proteinuria/hematuria or end-stage renal disease (ESRD). All patients' medical history data were obtained from regional hospitals and renal survival data from the national kidney register. Six (11%) of the 55 identified patients had developed ESRD. Sixteen (52%) of the 31 participants were not attending for regular follow-up visits after the acute phase. Twenty-two (71%) had renal symptoms and 12 (39%) were receiving drugs for hypertension/proteinuria at their latest follow-up visit. The chronicity index and total biopsy score in the first renal biopsy were higher in patients with persistent nephropathy or ESRD than in those without (p=0.022 and p=0.014, respectively). Nine (69%) of the 13 subjects who had been over 16 years of age at diagnosis had persistent nephropathy or ESRD, compared with 4 (22%) of the 18 subjects who had been under 16 years of age (relative risk 3.1, 95% CI 1.2-8.0). Pregnancy complications were common: 12 (55%) of the 22 pregnancies had been complicated by proteinuria and/or hypertension, and the prematurity rate was 30%. Long-term follow-up during adulthood is needed even after mild childhood IgA nephritis, especially in women during and after pregnancy.