BackgroundRenal cysts are uncommon among the pediatric population, and their transformation into malignant lesions is also uncommon. Early detection can prevent further complications and protect renal function. Bosniak classification is a computed tomography-based classification for renal cysts developed for adults. Children are more susceptible to CT radiation. Therefore, a modified Bosniak classification for children based on the ultrasound (US) can be used if it shows reliability and accuracy.AimTo apply the modified Bosniak classification system among children with renal cysts.MethodsThis was a retrospective study that was conducted on pediatric patients who underwent surgery for intermediate and high-risk complex renal cysts in Prince Sultan Military Medical City, Riyadh, Saudi Arabia using radiological information from 2009 to 2022. The collected data included demographics, medical history, radiological findings, and characteristics of renal cysts. SPSS Statistics v. 22 (IBM Corp., Armonk, NY) was used to analyze the data.ResultsThere were 40 children included in the study based on the US-modified Bosniak classification. Around 26.3% of patients had class I and 39.5% had class II renal cysts. Histopathology showed that 10% had Wilms tumor, and 15% had benign lesions. There were significant correlations between pathology findings and US findings (p=0.004), and CT findings (p=0.016).ConclusionThe modified Bosniak classification based on the US is sensitive, specific, and sufficiently accurate in the classification of renal cysts among children. Also, the size of the renal cysts can be a diagnostic marker of differentiation of benign and malignant cysts with high sensitivity and specificity.