Mammography practices were studied among a sample of 19,253 women aged 35 to 74 who underwent a periodic health examination (PHE). Mammography is common among women attending a PHE, even before the age of 50: 79.1% of women had had at least one mammogram at the time of the study; 47.3% had undergone this test as part of screening within the past three years. However, while screening mammography is very common before age 50 (45.8% among women aged 45–50), it reaches only 65.2% of the target population. Among the factors associated with this practice, multivariate analyses highlight in particular age (35–49 years versus 50–69 years: OR = 3.1), a first-degree relative with breast cancer (OR = 1.45), and regular gynecological follow-up (OR = 4.5). This study nevertheless highlights under-screening among young women with a family history of breast cancer or among women over 70 years of age, coexisting with high rates of individual screening before age 50. Furthermore, the frequency of screening mammograms is higher in departments where an organized screening program (OSP) is in place (71.4% versus 60.1% among women aged 50–69), although only 64% of women are aware of an OSP campaign in their department.