The aim of this prospective observational study was to verify the tolerability and safety profile of risperidone in a sample of antipsychotic-naive children/adolescent patients having a different psychiatric diagnosis. Twenty-two (mean age of 12±3.2) antipsychotic-naive patients who started therapy with risperidone were recruited. The assessment involved anthropometric data (weight, height, BMI, BMI z-score and BMI percentile), cardiovascular parameters (blood pressure and QTc interval) and blood tests (levels of glucose, triglycerides, total cholesterol, glutamic oxaloacetic and pyruvic transaminases, γ-glutamyl transferase, prolactin, free triiodothyronine, free thyroxine, thyroid-stimulating hormone, thyroglobulin, antithyroid peroxidase and antithyroglobulin). After an average follow-up of 6 months of risperidone therapy, a statistically significant increase in weight and body composition was observed. Furthermore, an increase in serum levels of prolactin was observed in 50% of patients. No other significant changes in metabolic and cardiovascular parameters were found. Although an increase in these parameters was detected, it remained in the normal range. This study suggests the use of specific protocols for monitoring children/adolescents treated with second-generation antipsychotics to manage the metabolic long-term complications and progression to more severe disease states.