The aim of this investigation was to identify factors that influenced or motivated women (N = 737) to donate human milk to human milk banks in Alagoas, Brazil. The most common characteristics of a regular donor were having 4 to 7 pregnancies (relative risk [RR] = 1.9285; 95% confidence interval [CI] = 1.0388-3.5800) and having obtained a higher education level (RR = 2,0625; 95% CI = 1.0097-4.2130). The most commonly reported reasons for donating were "encouragement of a health professional" (61.3%), followed by "the needs of the babies the banks serve" (25.3%). Most of the donors (49.9%) were introduced during their stay in the hospital to the human milk bank to which they donated, and 25.8% chose the bank recommended by a health professional. Health professionals play an indispensable role in motivating mothers to become human milk donors.