Although low fiber intake has been considered a risk factor for diverticulitis, prospective evidence is limited in women despite having a disproportionate burden of disease, with little known about variation in the protective effects according to food sources. We assessed the associations of intakes of fiber and major food sources of fiber including fruits and vegetables with risk of diverticulitis in a large cohort of women. We followed 50,019 women in the Nurses' Health Study (1990-2014) who were aged 43-70 years and free of diverticulitis, cancer, and inflammatory bowel disease at baseline. Incident diverticulitis was identified through self-report with validity confirmed by review of medical records. We documented 4,343 incident cases of diverticulitis, encompassing 1,106,402 person-years of follow-up. Compared with participants in the lowest quintile, the multivariable hazard ratio of diverticulitis in the highest quintile of total fiber intake was 0.86 (95% confidence interval: 0.78-0.95; P-trend = 0.002). Fiber from fruits and cereals, but not vegetables, was associated with a decreased risk of diverticulitis. Furthermore, intake of total whole fruit intake and specific fruits such as apples/pears and prunes were associated with reduced risk of diverticulitis with a multivariable hazard ratio for diverticulitis of 0.95 (0.92-0.98; P-trend < 0.001) for every serving increase of total whole fruit intake per day. Higher intake of dietary fiber and fiber from different food sources, except for vegetable fiber, are associated with a lower risk of diverticulitis in women. A greater intake of whole fruit is also associated with reduced risk.