Objective-To determine if preoperative hyponatremia in women with ovarian, fallopian tube (FT), and primary peritoneal cancers (PPC) is associated with postoperative complications. Methods-We performed a retrospective population-based cohort study of women with a postoperative diagnosis of ovarian, FT, or PPC who had a cytoreductive procedure in the National Surgical Quality Improvement Program (NSQIP) database from 2005-2013. The primary exposure, preoperative sodium, was classified as normal (135mEq/L-142mEq/L) or hyponatremic (≤134mEq/L). Where appropriate, preoperative characteristics were compared with Chi-squared or Fisher's exact tests. Multivariate logistic regression was used to determine adjusted odds ratios (aOR) with 95% confidence intervals (CI). Results-4009 subjects met inclusion criteria. Thirty day mortality was higher in the hyponatremic group compared to the normal serum sodium group (3.56% vs 1.18%). When patients of any age were noted to have at least two pertinent preoperative lab abnormalities, including hyponatremia, there was an increased risk of postoperative complications for patients over the age of 65. After adjusting for serum albumin and other confounders, preoperative hyponatremia was associated with an increased risk of hospital stay of >14 days (aOR 1.69; 95% CI 1.11-2.57) and 30 day postoperative mortality (aOR 2.37; 95% CI 1.13-4.98). Conclusions-Hyponatremia is associated with postoperative 30 day mortality and morbidity in women with ovarian, FT, and PPC. Serum sodium in conjunction with other markers may have the potential to identify candidates for neoadjuvant chemotherapy. Additional work is needed to determine if correction of hyponatremia in the preoperative period alters outcomes.