Axial involvement in psoriatic arthritis (axPsA) presents clinical and radiological differences from ankylosing spondylitis (AS), which may influence the therapeutic response. While Guselkumab has demonstrated efficacy in peripheral PsA, its role in axPsA is less well established, particularly in real-world settings. To evaluate the positive effects of Guselkumab therapy in patients with psoriatic arthritis (PsA), 58.6% of whom have axial involvement, in a 12-month, single-center, longitudinal, prospective observational cohort study conducted in a real-life setting. A cohort of 99 patients with PsA, including 58 with axial involvement (axPsA), was treated with Guselkumab for 12 months. Treatment efficacy was assessed by evaluating the reduction in mBASDAI, ASDAS, DAPSA, VAS Pain, LEI, and HAQ scores. The Friedman test was used to analyze whether the overall changes from baseline to 12 months were statistically significant. Patients with axial involvement were assessed by MRI, with scores measured at baseline (t), after 6 months (t), and after 12 months (t) of therapy. Statistical evaluation was conducted using the Friedman test, followed by pairwise comparisons of values obtained at different follow-up time points using the Wilcoxon signed-rank test. Additionally, the drug's retention rate was examined using a Kaplan-Meier curve. After 12 months of therapy, a statistically significant reduction was observed in all clinimetric parameters. Patients with axial involvement were also evaluated by MRI at baseline, after 6 months, and after 12 months of therapy. MRI images showed a reduction in bone marrow edema and a decrease in signal intensity, indicating a significant reduction in inflammation and confirming the drug's efficacy. Retention rate values demonstrate that Guselkumab is well tolerated and effective in the long term for the majority of patients. This 12-month real-world study of 99 PsA patients confirms the efficacy of Guselkumab in reducing disease activity in both peripheral and axial forms. The findings align with previous RWE and clinical trials (DISCOVER-1 and -2), supporting its clinical utility in PsA and axPsA, with high treatment retention.