Background Immunoglobulin A (IgA) vasculitis (also known as Henoch-Schonlein purpura) is the most common small vessel vasculitis of childhood. The long-term prognosis depends on renal involvement. The aim of this study was to evaluate the risk factors associated with renal involvement in children with IgA vasculitis and to investigate the best timing of urine examination to predict the presence of renal involvement at the sixth month after the diagnosis. Methods In this prospective observational study, medical records, demographic data, clinical findings, laboratory tests, and urine microscopic examinations of pediatric patients diagnosed with IgA vasculitis were evaluated to identify potential risk factors associated with renal involvement. Results A total of 178 patients with a median age of 6 years were involved in the study. Renal involvement was found in 24 (13.5%) patients. Most of the patients (85.7%), whose urine examination was found to be abnormal at the sixth month after the diagnosis, also had abnormalities in the first month urine examination. Factors significantly associated with renal involvement were as follows: older age, presence of hematuria and or proteinuria in the first month urine examination and patients who presented the disease in the spring season. Multivariate logistic regression analysis showed age >= 8 years (p = 0.005), the season of onset (p = 0.025), serum creatinine levels (p = 0.016), and abnormal urine examinations at the first-month visits (p = 0.005) significantly increased the risk of renal involvement. Conclusion This study has demonstrated that the optimal date to predict the presence of hematuria and/or proteinuria in the sixth month is the urine examination performed in the first month of the disease. Therefore, we think that patients with IgA vasculitis who show a presence of hematuria and/or proteinuria in the first-month urine examination should be followed more closely.