We compared the prognostic factors and outcome of 30 patients with juvenile chronic arthritis (JCA) extending into adult life with those of 30 patients with adult rheumatoid arthritis (RA) at a university adult rheumatology clinic; pairs were matched for sex and duration of disease (mean 8 years). One-third of JCA patients had seronegative polyarticular disease and another third had oligoarticular disease. In a third of the JCA patients, the clinical presentation changed during the follow-up. Over half of the RA patients had seropositive polyarticular and a one-third had seronegative polyarticular disease. Fewer seropositive patients were recorded in the JCA group than in the RA group both at the beginning (16.7% versus 56.7%; p=0.003) and at the end of the follow-up (14.3% versus 59.3%; p=0.001). JCA patients developed less radiographic changes than RA patients (46.7% versus 76.7%; p=0.034); oligoarthritis in the JCA group had the best prognosis whereas seropositive polyarthritis in the RA group had the worst prognosis. Significantly more patients with JCA than RA (60% versus 23%; p=0.009) were in remission at the end of the follow-up. In conclusion, when studied in adult life, the long-term prognosis is better in patients with JCA than in those with RA.