OBJECTIVE Gaining access to the pyelocaliceal system in percutaneous nephrolithotomy (PCNL) is routinely performed using fluoroscopic guidance with the patient in a prone position. We compared ultrasonography-guided access for PCNL with the patient in the flank position with conventional fluoroscopy-guided access. METHODS A total of 60 patients were randomly separated into two 30-patient groups--namely, ultrasonography-guided access with the patient in the flank position as group 1, and fluoroscopy-guided access with the patient in the prone position as group 2. In group 1, the entire procedure was performed under ultrasonography guidance. RESULTS Successful access was achieved 100% in both groups. The success rate was 86.7% in group 1 and 90% in group 2 (P = 0.45). The residual stone rate (stone >or=4 mm) was 13.3% in group 1 and 10% in group 2. The access duration was 14.5 +/- 2.6 minutes and 9.4 +/- 2.3 minutes in groups 1 and 2, respectively (P < 0.05). No significant differences for complications without any adjacent injuries were detected in both groups. Furthermore, the average hospital stay was 2.7 +/- 0.3 and 2.9 +/- 0.3 days accordingly for groups 1 and 2 (P = 0.89). CONCLUSIONS Ultrasonography has a high ability to access calculi more easily through the pyelocaliceal system with the patient in the flank position. It is convenient for urologists, and the return to the supine position is possible easily when necessary. Besides, PCNL under ultrasonography guidance and with the patient in the flank position has high success rates and limited complications; hence, we recommend this technique as an alternative procedure for fluoroscopy-guided PCNL.