OBJECTIVE: Analyze tofacitinib efficacy and safety by background methotrexate (MTX) dose in patients with psoriatic arthritis (PsA). METHODS: This post hoc analysis pooled data from two phase III, double-blind trials (OPAL Broaden, NCT01877668; OPAL Beyond, NCT01882439) including patients receiving tofacitinib 5 or 10 mg twice daily (BID), or placebo, with stable MTX. Efficacy outcomes at month 3 stratified by MTX dose (≤ 15 month 3 stratified by MTX dose vs > 15 mg/week) were American College of Rheumatology (ACR)20/50/70, Health Assessment Questionnaire-Disability Index (HAQ-DI); Psoriasis Area and Severity Index (PASI)50/75; change from baseline in HAQ-DI; physician's global assessment of PsA (PGA-PsA-visual analog scale [VAS]); patient's global joint and skin assessment (PGJS-VAS), Leeds Enthesitis Index (LEI); and Dactylitis Severity Score (DSS). Safety assessments included adverse events and laboratory parameters. RESULTS: Five hundred fifty-six patients received tofacitinib 5 mg BID (n = 186), 10 mg BID (n = 178), or placebo (n = 192), plus MTX (≤ 15 mg/week, n = 371; > 15 mg/week, n = 185). At month 3, tofacitinib efficacy was generally greater than placebo. Patients receiving tofacitinib 5 mg BID demonstrated greater numerical improvements in efficacy outcomes at month 3 with MTX > 15 mg/week vs MTX ≤ 15 mg/week; patients receiving tofacitinib 10 mg BID displayed the opposite. The safety profile was generally consistent between groups; headache was associated with MTX > 15 mg/week; decreased hemoglobin levels were observed in patients receiving tofacitinib 10 mg BID and MTX ≤ 15 mg/week. CONCLUSION: Efficacy of tofacitinib was generally numerically greater than placebo, regardless of MTX dose. Tofacitinib 5 mg BID was generally more efficacious with MTX > 15 mg/week vs ≤ 15 mg/week; the opposite was observed for tofacitinib 10 mg BID. Headache was more frequent with MTX > 15 mg/week. TRIAL REGISTRATION: ClinicalTrials.gov . Identifier: NCT01877668 (registration: June 14, 2013) and NCT01882439 (registration: June 20, 2013). Key Points • Methotrexate is widely used in the treatment of psoriatic arthritis; however, there are limited data on the impact of varying background methotrexate doses on the efficacy and safety of Janus kinase inhibitors in patients with psoriatic arthritis. • This post hoc analysis assessed the impact of background methotrexate dose (≤ 15 or > 15 mg/week) on tofacitinib efficacy and safety in patients with psoriatic arthritis. • Results indicated that tofacitinib efficacy was generally numerically greater than placebo, regardless of methotrexate dose. Tofacitinib 5 mg twice daily, in combination with a higher dose of background methotrexate, was more efficacious compared with a lower dose of background methotrexate; the opposite was observed for tofacitinib 10 mg twice daily. • Headache was more frequent with the higher methotrexate dose. Data should be interpreted with caution due to the small sample sizes.