This phase 2/3, double-blind, placebo-controlled study was designed to assess the safety and efficacy of ustekinumab in Japanese patients with moderate-to-severe plaque-type psoriasis. Overall, 158 patients were randomized to receive ustekinumab 45 or 90 mg at weeks 0, 4, and every 12 weeks, or placebo with cross-over to ustekinumab at week 12. The primary end-point was the proportion of patients achieving at least 75% improvement in Psoriasis Area and Severity Index (PASI 75) at week 12. Physician’s Global Assessment (PGA), Dermatology Life Quality Index (DLQI), Nail Psoriasis Severity Index and joint pain Visual Analog Scale (VAS) were also measured. At week 12, 59.4% and 67.7% of ustekinumab 45 and 90 mg patients achieved PASI 75, respectively, compared with 6.5% in the placebo group (P < 0.0001 each). PASI 75 responses were maintained through week 64 in 65.0% and 78.6% of the ustekinumab-treated patients, respectively. Placebo cross-over patients had similar responses to ustekinumab-treated patients. Significant improvements in PGA, DLQI and VAS scores were observed at week 12 and generally maintained over time. Adverse events during the placebo-controlled period were similar among groups (45 mg, 65.6%; 90 mg, 59.7%; placebo, 65.6%). Serious adverse events were observed in 0%, 4.8% and 6.3% of patients, respectively. Through week 72, similar rates and types of adverse events and serious adverse events were reported in patients receiving 45 and 90 mg. Rates of injection site reactions and antibodies to ustekinumab were low. Ustekinumab was efficacious and generally well-tolerated in Japanese patients with moderate-to-severe plaque-type psoriasis through 72 weeks. These results are consistent with those reported in the global, phase 3 studies.