Little information is available from real-life studies evaluating the efficacy of guselkumab in moderate-to-severe psoriasis. In this real-life study, we retrospectively examined a database of 52 patients with moderate-to-severe psoriasis treated with guselkumab (100 mg, s.c.) and followed for 1 year. Disease severity and treatment response was assessed by the Psoriasis Area and Severity Index (PASI) at baseline and after 4, 12, 20, 28, 36, 44, and 52 weeks. Predictors of a PASI response were evaluated by univariate and multivariate regression. After 12 months, 84.2% of patients (mean age 51.3 ± 14.1 years) treated with guselkumab achieved a PASI score of <3. Furthermore, PASI score decreased from 20 ± 13.3 at baseline to 4.4 ± 4.7 and 2.7 ± 3.9 at 12 and 20 weeks, and PASI 75, 90, and 100 response was achieved in 84.2%, 78.9%, and 63.2% of patients respectively at 12 months. Stepwise multivariate regression analysis revealed that previous biological treatment and the presence of comorbidities were associated with poorer response between 28–44 weeks, however the presence of obesity per se was not associated with poorer response. Difficult-to-treat areas were also improved as early as 12 weeks following guselkumab. Guselkumab was observed to be effective and safe in patients with moderate-severe chronic psoriasis in a real world-setting.