Joint manifestations observed during the course of a prospective RA 27/3 rubella immunisation trial were compared with those observed during an intercurrent wild rubella epidemic in an outlying community. Among 44 rubella haemagglutination inhibition (HAI) negative females ranging in age from 17 to 33 years who received rubella vaccine, six (13.6%) developed acute polyarticular arthritis within two to four weeks postvaccine and two (4.5%) had continuing or recurrent arthropathy lasting longer than 18 months. In contrast, among 23 females ranging in age from 11 to 39 years undergoing wild rubella infection, 12 (52.2%) developed acute polyarticular arthritis and seven (30.4%) had recurrent arthropathy 18 months postinfection. Among 23 males ranging in age from 13 to 54 years undergoing wild rubella infection, only two (8.7%) developed acute arthritis and both individuals had continuing joint manifestations 18 months postinfection. Wild rubella infection in adult populations is associated with a higher incidence, increased severity, and more prolonged duration of joint manifestations than is seen after RA 27/3 rubella immunisation.