Although several studies have found screen-detected cancers in women with familial breast cancer risk have favorable prognostic features compared with symptomatic cancers, the impact of level of familial risk is unknown. A cohort of 899 first-degree female relatives of cases of breast cancer from the Ontario site of the Breast Cancer Family Registry was followed for 2 years. Logistic regression analyses compared diagnoses of breast cancer or benign breast disease (BBD) between women at high (n = 258, 28.7 %) versus low/moderate (n = 641, 71.3 %) familial risk. Similar analyses compared prognostic features of invasive cancers and BBD by level of familial risk and mammography screening status. Among 899 women, 44 (4.9 %) were diagnosed with invasive breast cancer and/or ductal carcinoma in situ, and 56 (6.2 %) with BBD. Women with high familial risk were significantly more likely to be diagnosed with breast cancer [odds ratio (OR) = 2.84, 95 % confidence interval (CI) 1.50-5.38] than low/moderate risk women, particularly if diagnosed at age ≥50 (OR = 2.99, 95 % CI 1.37-6.56) or screened with mammography (OR = 3.33, 95 % CI 1.54-7.18). High risk women were more likely to be diagnosed with BBD (OR = 1.94, 95 % CI 1.03-3.66). Level of familial risk was not associated with prognostic features. Cancers among unscreened women were larger (OR = 9.72, 95 % CI 1.01-93.61) and diagnosed at stage II or above (OR = 7.80, 95 % CI 1.18-51.50) compared with screen-detected cancers. Screening mammography may be effective for women with a first-degree family history of breast cancer, irrespective of level of familial risk.