Nationwide register data provide unique opportunities for real-world assessment of complications from different surgical methods. This study aimed to assess incidence of, and predictors for, post-operative complications and to evaluate 90-day mortality following different surgical procedures and thermal ablation for renal cell carcinoma (RCC). All patients undergoing surgical treatment and thermal ablation for RCC in Sweden during 2015-2019 were identified from the National Swedish Kidney Cancer Register. Frequencies and types of post-operative complications were analysed. Logistic regression models were used to identify predictors for 90-day major (Clavien-Dindo grades III-V) complications, including death. The overall complication rate was 24% (1295/5505), of which 495 (8.7%) were major complications. Most complications occurred following open surgery, of which bleeding and infection were the most common. Twice as many complications were observed in patients undergoing open surgery compared to minimally invasive surgery (20% vs. 10%, P < 0.001). Statistically significant predictors for major complications irrespective of surgical category and technique were American society of anesthiologists (ASA) score, tumour diameter and serum creatinine. Separating radical and partial nephrectomy, surgical technique remained a significant risk factor for major complications. Most complications occurred within the first 20 days. The overall 90-day readmission rate was 6.2%, and 30- and 90-day mortality rates were 0.47% and 1.5%, respectively. In conclusion, bleeding and infection were the most common major complications after RCC surgery. Twice as many patients undergoing open surgery suffer a major post-operative complication as compared to patients subjected to minimally invasive surgery. General predictors for major complications were ASA score, tumour size, kidney function and surgical technique.