The current prospective observational study aimed to evaluate the long-term (24 months), real-life effectiveness of ustekinumab in psoriatic arthritis (PsA). Consecutive patients with moderate-severe PsA and active psoriasis who begun ustekinumab treatment were evaluated prospectively (January 2015-March 2017). Clinimetric scores and biochemical values were assessed at baseline (T0), at 6 (T6), 12 (T12), and 24 (T24) months. Friedman test and generalized linear models were used to compare variables over time. Regression analysis to identify determinants of minimal disease activity (MDA) at T6 and of treatment discontinuation was conducted. Sixty-five patients (43.1% men; age 49.4 ± 11.6 years) were enrolled; ustekinumab was prescribed as a first (20%), second (33.8%), third (26.5%), fourth (15.4%), or fifth (4.6%) line biological therapy. Significant decrease in tender/swollen joints, Visual Analogue Scale of pain (VASp) and general health (VASgh), Disease Activity in PsA (DAPSA), Psoriasis Area Severity Index (PASI), Leeds Enthesitis Index (LEI), Health Assessment Questionnaire modified for spondyloarthritis (HAQ-S), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) was achieved. MDA was reached by 30.7, 47.0, and 34.0% of patients respectively at T6, T12, and T24. In multivariable models, mono-oligoarthritis was independently associated to MDA at T6 (OR 9.02; 95% CI 1.41, 57.71), while baseline CRP (OR 1.12; 95% CI 1.00, 1.26) and LEI (OR 0.50; 95% CI 0.25, 0.97) to ustekinumab discontinuation. More patients used disease-modifying antirheumatic drugs at T0 (35.3%) than at T24 (8.5%). Only nine episodes of infection and no serious adverse events were registered. In a real-life clinical setting, ustekinumab was safe and effective in PsA. Comedication tapering was often possible.