Rituximab has been approved in Japan for the treatment of intractable nephrotic syndrome, but in cases of childhood-onset disease only; its efficacy and safety in adult-onset disease has yet to be established. This study was undertaken to evaluate the efficacy of rituximab and adverse effects in patients with adult-onset minimal change nephrotic syndrome (MCNS).The study involved 32 childhood-onset cases (mean age at onset: 8.6 years) and 19 adult-onset cases (mean age at onset: 30.6 years) of frequently relapsing steroid-dependent MCNS, all of whom received intravenous rituximab drip infusion (375 mg/m body surface area per dose) at 4 time points at 6-month intervals. Relapse frequency, oral dose of immunosuppressants, and adverse effects were compared between the 2 groups.Remission was maintained in all cases in the childhood-onset and adult-onset groups; a significant reduction in relapse frequency was noted during the first 24 months of rituximab therapy (0.3 ± 0.7 times and 0.3 ± 0.6 times in the childhood-onset and adult-onset groups, respectively; P < .001). Oral corticosteroid therapy could be discontinued in 81.3% of cases of the childhood-onset group (26/32 cases) and in 70.6% of cases of the adult-onset group (12/17 cases); the oral corticosteroid dose was reduced significantly to 0.9 ± 2.5 mg/day in the childhood-onset group and to 0.8 ± 1.6 mg/day in the adult-onset group (P < .001). Cyclosporin treatment was also discontinued in 87.5% of cases in the childhood-onset group (21/24 cases) and in 80.0% of cases of the adult-onset group (15/21 cases); the oral cyclosporin dose was reduced significantly to 8.6 ± 27.4 mg/day and 9.2 ± 22.0 mg/day, respectively (P < .001). Regarding adverse reactions, infusion reactions developed at a frequency of 21.1% and 19.7% in both groups, respectively, with no significant inter-group difference (P = .72).Rituximab showed significant efficacy in adult-onset MCNS, with a comparable incidence of adverse reactions to that in childhood-onset cases, suggesting that this drug can also be used safely in adult-onset MCNS.