Background: Accurate and swift tissue diagnosis is extremely important for the timely initiation of treatment in pediatric oncology. In our department, ultrasound guided core needle biopsy (US guided CNB) is used for tissue diagnosis. In 2016, we added on-site cytology, allowing for an immediate primary diagnosis. We retrospectively reviewed our performance in terms of safety and accuracy for CNBs and on-site cytology Procedure: All pediatric biopsies performed in our hospital between February 2016, and December 2019 were included. Patient clinical, procedural and follow up data were collected. CNB pathology and cytology results were compared to final pathologic diagnosis. Results: We included 185 patients for which 210 biopsies were performed; Median latency time to biopsy was one day. Altogether, we had 164 tumors, (148 malignant,16 benign) and 46 other lesions. 159 tumors were correctly diagnosed by CNB; five malignant tumors were misdiagnosed as benign. The sensitivity of our US guided CNB is 96.7%, specificity 100%, and accuracy 97.6%. On-site cytology was performed in 41 cases; 36 malignant tumors, 2 benign tumors and 3 reactive lymph nodes. The cytologist correctly differentiated tumor from inflammation in all cases, and diagnosed the precise tumor type in 38 cases, with accuracy of 93% for final diagnosis. We had no complications related to the procedure or sedation. Conclusions: US guided CNB with on-site TI cytology for suspected malignancy in the pediatric population highly available, safe and accurate, with real time diagnosis in most cases. The accelerated diagnostic root has huge impact on patient care.