Objective: This study aimed to compare the effects of bladder diverticula smaller than 30 (SD) mm and larger than 30 mm (LD) on bladder functions and urodynamics. Materials and methods: Our retrospective analysis involved a cohort of 40 pediatric patients diagnosed with primary bladder diverticula. Results: The predicted mean bladder capacity (MBC) was 197.7 ± 95.8 mL, whereas the observed MBC was lower at an average of 170.1 ± 79.6 mL. This indicates that the observed MBC was 88.2 ± 12.9% of the predicted value (percentage). The mean diverticula diameter recorded was 33 ± 19.5 mm, and the diverticula to MBC ratio were calculated to be 0.25 ± 0.18. The distribution of urinary tract infections (UTIs) differed significantly between the groups (p < 0.001). Upper UT dilatation was significantly more common in the LD group (60%, n = 12) than in the SD group (15%, n = 3) (p = 0.003). The mean detrusor pressure (P[detrusor]) was significantly higher in the LD group (137.2 ± 24.1 cm H 2 O) than in the SD group (63.9 ± 5.8 cm H 2 O) (p = 0.001). In addition, the mean peak flow rate (Q max ) was significantly higher in the SD group (20.7 ± 7.9 mL/s) compared to the LD group (12.7 ± 3.8 mL/s) (p < 0.001). Conclusion: Bladder diverticula size is a significant factor in the clinical presentation and management of primary bladder diverticula in pediatric patients.