Although infliximab is approved for psoriasis, its efficacy is reduced over time in some patients. The aim of this phase III trial is to evaluate efficacy and safety of infliximab dose escalation in Japanese psoriasis patients with loss of efficacy to standard-dose therapy. Patients with plaque psoriasis, psoriatic arthritis, pustular psoriasis or psoriatic erythroderma who showed loss of efficacy to standard-dose therapy received infliximab dose escalation (10 mg/kg every 8 weeks) from weeks 0 to 32. Loss of efficacy was defined as not maintaining 50% reduction in the Psoriasis Area and Severity Index (PASI 50) after achieving PASI 75. Efficacy and safety were evaluated up to week 40. Fifty-one patients received dose escalation and 43 completed the study. PASI 75 and median improvement rate of PASI score at week 40 were 44% and 70.0%, respectively, showing efficacy in skin symptoms. Efficacies in quality of life, nail psoriasis and joint pain were also obtained. Median serum infliximab level increased from less than 0.1 to 1.1 μg/mL from weeks 0 to 40, showing positive correlation between efficacy and serum infliximab level at week 40. Favorable efficacy was observed in patients with detectable serum infliximab levels (≥0.1 μg/mL) at baseline. Incidences of adverse events, serious adverse events, serious infections and serious infusion reactions were 92%, 10%, 4% and 0%, respectively. No marked difference was observed in both efficacy and safety among psoriasis types. No new safety concerns were observed. Infliximab dose escalation was effective and well-tolerated in psoriasis patients with loss of efficacy to standard-dose therapy, suggesting that dose escalation may be a useful therapeutic option for these patients.