Body mass index and waist–hip ratio are related to human health and both play a role in mate choice. However, previous research is inconsistent as to what body mass index and waist–hip ratio values are preferred in women and what the relative importance of body mass index and waist–hip ratio for attractiveness is. Here, we made several methodological refinements to obtain reliable estimations. Participants (Poles) indicated the most attractive woman from a set of digitally manipulated high-quality silhouettes varying orthogonally in body mass index and waist–hip ratio and viewed from behind to exclude effects of the breast size. Then, each participant chose the more attractive silhouette from pairs in which one figure deviated from his/her ideal in body mass index and the other in waist–hip ratio. Both sexes preferred underweight women (body mass index = 17.3) with accentuated waist (waist–hip ratio = 0.66 for female and 0.70 for male judges). These represent preferences for unhealthy body mass and healthy body shape. Furthermore, body mass index proved twice as important for attractiveness as waist–hip ratio, even though literature data indicate that waist–hip ratio is at least as important for health as body mass index. We discuss the obtained pattern of preferences from the perspective of evolutionary psychology.