Aim: Assessment of the correlation between high body mass and metabolic causes of urolithiasis in patients treated over a 2-year period in the Department of Paediatrics, Paediatric Nephrology and Allergology at the Military Institute of Medicine in Warsaw. Material and methods: A total of 109 children with urolithiasis, aged 9–18 years (mean: 13 years), were enrolled in the study. The patients were divided into two groups: Group I – children with normal body mass (body mass index <85^th percentile), and Group II – children with high body mass (body mass index ≥85^th percentile). Group I consisted of 74 children (33 girls and 41 boys). Group II comprised 35 children (23 girls and 12 boys). Blood serum and urine samples were collected and tested in the laboratory to determine the causes of urolithiasis. In addition, anthropometric parameters were evaluated, including body mass index, waist circumference, waist-to-hip ratio, body mass, and body height. Also, the lipid profile was examined, and arterial blood pressure was measured in the study subjects. Results: Children with high body mass were found to have statistically significantly higher serum uric acid levels [5.4 mg/dL (5.0–6.2) vs. 4.7 mg/dL (4.1–5.4); p < 0.05] and statistically significantly higher urinary uric acid excretion (determined on the basis of the uric acid/creatinine ratio in second morning urine) compared to children with normal body mass [0.3 (0.2–0.3) vs. 0.2 (0.2–0.3); p = 0.01]. There were no statistically significant differences in the excretion of other crystalloids. In addition, children with high body mass were shown to have significantly higher values of total cholesterol [167.5 (142.0–183.0) vs. 152.0 (136.0–163.0); p < 0.05], LDL [103.5 (83.0–117.5) vs. 88.5 (69.0–102.0); p < 0.05], and triglycerides [104.0 (89.0–111.0) vs. 64.0 (52.0–106.0); p < 0.05] as well as lower mean vitamin D levels (26.6 mg/dL ± 9.25 vs. 22.6 mg/dL ± 6.75; p = 0.04), and higher systolic blood pressure (110.2 mm Hg ± 11.0 vs. 115.7 mm Hg ± 11.96; p = 0.02) compared to non-overweight children. Conclusions: There is a possible correlation between overweight and urolithiasis associated with excessive uric acid excretion. Overweight patients with urolithiasis present disorders in the lipid profile which may have an impact on the formation of calculi. Lower serum vitamin D concentrations in overweight patients do not affect the level of calciuria.