Alopecias are traditionally categorized by the presence or absence of scarring and by a diffuse or localized pattern. A common clinical conundrum is that of a woman presenting with the chief complaint of diffuse, nonscarring hair loss. We review the 4 main diagnostic possibilities for this clinical scenario: (1) female pattern hair loss (androgenetic alopecia), (2) acute and chronic telogen effluvium, (3) diffuse alopecia areata, and (4) loose anagen syndrome. We also outline our approach to the individual patient, emphasizing the pertinent history, physical examination, and appropriate diagnostic testing. This approach usually allows the clinician to make a definitive diagnosis or limited differential diagnosis and to offer the patient therapeutic options. (J Am Acad Dermatol 2002;47:809-18.) Learning objective: At the completion of this learning activity, participants should be familiar with the diagnostic possibilities in evaluating diffuse, nonscarring hair loss in women.