Objectives <p>To describe a rare case of sulfadiazine-associated nephrolithiasis in an infant treated for congenital toxoplasmosis and to highlight the clinical implications for monitoring and management during prolonged therapy.</p> Methods <p>This study describes a single case report of an 11-month-old male infant diagnosed with congenital toxoplasmosis who developed fever, urinary tract infection, bilateral nephrolithiasis (maximum diameter approximately 1.2&#xa0;cm), hydronephrosis, and renal dysfunction after 9 months of continuous treatment with sulfadiazine, pyrimethamine, and folinic acid.</p> Results <p>Following discontinuation of sulfadiazine and administration of intravenous antibiotics and supportive care, renal function normalized and the stones nearly resolved.</p> Conclusions <p>This case underscores the potential for severe urological adverse effects associated with sulfadiazine therapy in infants. Close monitoring of renal function and urinary ultrasound should be undertaken during prolonged sulfadiazine therapy.</p>