Purpose We assessed the relationship of surgical margins across different surgical approaches to partial nephrectomy in patients with clinical T1a renal cell carcinoma in a population based cohort. Materials and Methods We used NCDB (National Cancer Database) to identify all patients who underwent partial nephrectomy for clinical T1a renal cell carcinoma (tumor size less than 4 cm) from 2010 to 2011. The primary outcome was surgical margin status in patients treated with partial nephrectomy by the open, laparoscopic or robotic approach. Multivariable logistic regression analysis was done to identify patient, hospital and surgical factors associated with positive surgical margins. Results Partial nephrectomy was done in 11,587 patients, including open, laparoscopic and robotic nephrectomy in 5,094 (44%), 1,681 (14%) and 4,812 (42%), respectively. Mean ± SD age was 56 ± 12 years. Overall 806 patients (7%) had positive surgical margins. The positive surgical margin prevalence was 4.9%, 8.1% and 8.7% for the open, laparoscopic and robotic approaches, respectively (p <0.001). Laparoscopic and robotic partial nephrectomy had a higher adjusted OR for positive surgical margins (OR 1.81 and 1.79, respectively, each p <0.001) than open nephrectomy. When stratified by hospital type, differences in positive surgical margin rates remained, such that patients treated at academic medical centers who underwent laparoscopic and robotic partial nephrectomy had a higher adjusted OR (1.38, p = 0.074 and 1.73, p <0.001, respectively) than patients treated with open partial nephrectomy. Conclusions Laparoscopic and robotic partial nephrectomy is associated with higher positive surgical margin rates compared to open partial nephrectomy for clinical T1a renal cell carcinoma. The effect of margin status on long-term oncologic outcomes in this context remains to be determined.