The labeling practices of 390 facilities that consecutively submitted screening mammography images (mediolateral oblique and craniocaudal views) to the American College of Radiology (ACR) Mammography Accreditation Program over a 2-month period were evaluated. Methods for identifying the patient and facility included a flash card at 333 facilities (85%), stick-on paper labels at 54 (14%), and handwriting directly on the film at three (1%). Identification labels included the patient's first and last name at 372 facilities (95%), the date at 370 (95%), the name of the facility at 349 (89%), a unique patient identification number at 328 (84%), the patient's age at 169 (43%), the name of the referring physician at 146 (37%), and the patient's date of birth at 129 (33%). Labeling practices, information provided, and methods used varied considerably from one site to another. Adoption of ACR guidelines for labeling mammography films is encouraged.