Introduction/hypothesis: To estimate the effect of weight loss on fecal incontinence (FI) severity among overweight and obese women with urinary incontinence, we analyzed data from women randomized to a weight loss intervention or control condition. Methods: The modified Fecal Incontinence Severity Index (FISI) was administered at 6, 12, and 18 months in 338 women. Repeated measures analyses identified factors associated with improved FISI scores among women with baseline scores >0. Results: FISI scores improved in 45 (13%) across all time points among the 291 women (87%) completing the trial. Improved scores were associated with a one-point lower urinary tract symptoms (LUTS) score, p<0.01. Improved liquid stool FI frequency was associated with ≥5 kg weight loss (p=0.001), 10-g increase in fiber intake (p=0.05), and decreased LUTS (p=0.003). Conclusions: FI severity improved with weight loss. Women with liquid stool FI losing at least 5 kg and/or increased dietary fiber intake had improved FI frequency. © 2011 The International Urogynecological Association.