Background: Surveillance is a standard management option for clinical stage I testicular cancer. Serial CT imaging of the abdomen and pelvis (CTA/P) is a key component of all surveillance protocols. Standard dose CTA/P may result in a radiation exposure of up to 20 mSv and the cumulative exposure to ionizing radiation may have a carcinogenic effect over the lifespan of these young patients who are all cured of their disease. This study evaluated the safety of using low dose CT scans in this setting. Methods: Between 2005 and 2010, 239 patients (193 seminoma, 46 nonseminoma) with stage I testicular cancer were enrolled into a prospective phase II study and initially underwent standard dose CTA/P and low dose CTA/P (40-60% dose reduction). Patients continued with low dose CT alone if image quality was adequate (only 1 patient had poor quality images that could not be used for surveillance). Relapse in the retroperitoneum detected on low dose CT was confirmed with standard dose CT. These CT images were prospectively evaluated by a single radiologist to compare nodal size/number between the 2 imaging techniques. Results: Median age of patients was 36 years (range 18-83) and median follow up was 26 months (range 1-80). There were 32 relapses: 30 in retroperitoneal lymph nodes, 1 with raised serum tumour markers, and 1 in lung alone. Of the 30 nodal relapses, 28 pairs of CTs were assessed for nodal size. Mean size of retroperitoneal nodal relapse (short axis) was 16.9 mm and 16.6 mm for standard and low dose CT, respectively (p=0.28; 95% CI 0.61-0.82). In all cases there was ≤2 mm difference in the nodal size between the imaging techniques. Conclusions: Low dose CT scans may safely reduce radiation exposure due to retroperitoneal imaging during surveillance of stage I testicular cancer with minimal loss of diagnostic quality. The use of this imaging technique should be considered in all surveillance protocols.