Background: Approximately 30 – 60% of patients with mNSGCT treated with cisplatin-based chemotherapy (CBCT) achieve a complete response (CR), defined as normalization of serum tumor markers with either no RRM or a RRM < 1 cm. While there is universal agreement that patients with a RRM ≥ 1 cm should undergo retroperitoneal lymph node dissection (RPLND), many institutions, including ours, recommend surveillance for patients who achieve a CR. However, studies have not defined which axis of the RRM should be considered when making this decision. Methods: The electronic medical records (2007 – 2017) at the Hospital of the University of Pennsylvania (HUP) were searched to identify good-risk mNSGCT patients treated with CBCT who achieved a CR and underwent surveillance. Consistent with RECIST 1.1, we define a CR as no RRM or a RRM < 1 cm in the transaxial short axis (TSA). We do not consider the transaxial long axis (TLA) or the craniocaudal axis (CCA). A post-hoc review was performed by a blinded radiologist and the RRM dimensions in the TSA, TLA, and CCA were recorded. Differences in the frequency of recurrence between groups with a RRM < 1.0 cm and ≥ 1.0 cm in the TLA and CCA were assessed using the Fischer exact test. Results: 39 patients met study criteria and were included. At a median follow-up of 50.8 months, only 2 patients (5.1%) recurred. Both were successfully treated with RPLND and salvage chemotherapy. Post-hoc review of imaging: median TSA 6 mm (range, 0-11); median TLA 8 mm (range, 0-14); median CCA 11 mm (range, 0-34). Thirteen (33%) and 27 (69%) patients had a RRM ≥ 1 cm in the TLA and CCA, respectively. There were no statistically significant differences in the risk of recurrence between patients with a RRM < 1.0 cm and ≥ 1.0 cm in the TLA (p=0.54) or CCA (p=0.53). Conclusions: Surveillance is an effective strategy in patients with mNSGCT and a post-chemotherapy RRM < 1.0 cm in the TSA. Our study suggests that referencing the TSA and not the TLA or CCA in this decision-making may avoid unnecessary post-chemotherapy RPLND.