We assessed the role of standing vs supine scrotal ultrasound (SUS) for varicocele assessment by evaluating differences in clinical outcomes. We retrospectively reviewed men from 2008-2020 diagnosed with varicocele who had documented SUS with both supine and standing assessments with and without Valsalva. Clinical outcomes (semen parameters, TUNEL and serum testosterone [T]) after microsurgical varicocelectomy were compared among men who had varicoceles diagnosed by standing SUS (vein size >2.5 mm, vein size >3.0 mm or reversal of flow) to those who would have been missed on supine SUS only. A total of 349 men underwent varicocelectomy (right: 5 [1.4%]; left: 118 [33.8%]; bilateral: 226 [64.8%]). Disagreement between those with abnormal standing vs normal supine for vein size >2.5 mm was: 56 men (16.1%) on the right and 31 men (8.9%) on the left, for vein size >3.0 mm was: 64 men (18.3%) on the right, and 56 men (16.1%) on the left, and for flow reversal was: 36 (14.0%) on the right and 40 (15.4%) on the left. For those >2.5 mm, only T had significant improvements on the left (p=0.05). For those >3.0 mm significant differences were seen for sperm motility on the right (p=0.04), and TUNEL (p=0.04) and T (p <0.01) on the left. For flow reversal, significant differences were seen for sperm concentration (p <0.01), morphology (p=0.03) and volume (p=0.05) on the right and TUNEL on the left (p=0.02). Standing SUS identifies a greater number of men who would have been missed using supine SUS only.