Background <p>Kidney biopsies are common diagnostic procedures. Risk factors for biopsy complications in children are not well delineated. The objective of our study is to assess complication rates in pediatric native and transplant kidney biopsies and associated clinical and technical risk factors.</p> Methods <p>Our retrospective study at BC Children’s Hospital (Vancouver, Canada) included 402 biopsies performed on 232 patients from 2010–2018. Data were obtained through patient chart review. Minor complications were defined as perinephric hematomas ≥ 2&#xa0;cm or labelled as at least “moderate”, arteriovenous fistula, or pseudoaneurysm. Major complications were defined as complication requiring blood transfusion, embolization, or surgery.</p> Results <p>There were 32 biopsy complications (8%) of which one was a major complication. The most common complication was hematoma in native kidneys, and arteriovenous fistula in transplant kidneys. Complications rates were significantly higher in children &lt; 3&#xa0;years of age (22%, <i>p</i> = 0.046), female patients (11%, <i>p</i> = 0.048), patients with eGFR ≤ 30&#xa0;ml/min/1.73&#xa0;m² (17%, <i>p</i> = 0.025), hemoglobin &lt; 10&#xa0;g/dL (16%, <i>p</i> = 0.002), vasculitis (15%, <i>p</i> = 0.004), and native kidney biopsies (11%, <i>p</i> = 0.027). Most technical factors such as number of biopsies per patient, cortical tangential vs. perpendicular approach, training level, kidney location, and sedation methods were not associated with increased complication rates.</p> Conclusions <p>Kidney biopsies are a relatively safe procedure, especially in transplant patients. Specific patient populations (children &lt; 3&#xa0;years, patients with low eGFR, anemia, and vasculitis/SLE) may be at higher risk of complications. Standardization of biopsy protocol and complication definition will enhance consistency of outcome reporting and allow evidence-based improvement in biopsy practices.</p> Graphical abstract <p></p>