Surgical site infections (SSIs) occur in 10–15% of patients and are linked to up to 29% of delays in starting adjuvant treatment. This study assessed the association between SSIs in patients with ovarian and uterine cancer and their impact on time to adjuvant therapy and oncologic outcomes. Patients who underwent surgery from 1 January 2015 to 30 September 2017 were included, using institutional National Surgical Quality Improvement Program (NSQIP) data and chart reviews. Among 371 patients (median follow-up 4.1 years), 243 (65.5%) received adjuvant treatment. The median time to start was 39 days for chemotherapy, 61 days for radiotherapy, and 42 days for combined therapy (p < 0.001). Patients with ovarian cancer began treatment sooner than those with uterine cancer (39 vs. 52 days, p < 0.001), but no significant difference was observed between those with or without SSIs. In 238 patients with uterine cancer, those with SSIs had a twofold higher recurrence risk (HR 1.97, p = 0.022) and over threefold lower overall survival (HR 3.45, p = 0.018). Multivariable analysis showed that surgical route and disease stage were independent predictors; SSI was not an independent factor. No survival difference related to SSIs was found in patients with ovarian cancer. Further research is needed to clarify the impact of SSIs on treatment timing and recurrence.