METHODS In the mass bacille Calmette-Guérin (BCG) vaccination programme using the multipuncture method practised in Japan for young children, lymph node swelling is a not uncommon complication and its management is sometimes unnecessarily radical. OBJECTIVE To determine the frequency of lymphadenitis after BCG vaccination with the multipuncture method, and to describe its clinical features. METHODS A total of 34,516 children aged 0-3 years, who received primary vaccination with BCG between 1985 and 1989, were observed for the occurrence of lymphadenopathy. Oral explanation was given to the parents about lymph node swelling, and a postcard with a reporting form was given, to be returned if any lymph node swelling was observed in the baby. The parents were then contacted, and invited to our clinic for further observation. Cases with one or more swollen nodes greater than 7 mm were included in this analysis as cases of lymphadenopathy. RESULTS The frequency of lymphadenopathy was 0.73% (95% CI 0.65-0.83). Babies under 1 year of age had higher incidence. Lymph nodes greater than 10 mm were seen among 0.40% of babies, with a higher rate among boys than in girls (0.95% and 0.50%, respectively). Sixty-five percent of the cases were first noticed 4-6 weeks after vaccination; others were detected before or after that period. Nineteen percent of the cases had multiple swollen nodes, and 2% had adenitis only outside the axilla. Eight cases progressed to suppurative adenitis with rupture, comprising 0.02% (95% CI 0.012%-0.046%) of those vaccinated. In the remaining cases the swelling subsided quickly (92% within 2 months and the others later), with no medical or surgical treatment.