Females are at risk for body image and eating disturbance when they internalize societally prescribed standards of Western beauty. With respect to messages to be thin or muscular, numerous scales are available that measure internalization. However, many women are now receiving messages about the desirability of being both thin and toned, yet no self-report measure of internalization of a fit female body ideal exists. Our aim was to develop a multidimensional tool (i.e., the Fit Ideal Internalization Test; FIIT) useful for assessing women's internalization of the fit ideal (i.e., a lean and toned body ideal). Three studies were conducted, recruiting independent groups of women attending university to complete surveys. In Study 1 (N = 300, age 16-51), women completed the FIIT items, and a 3-factor structure of fit idealization (8 items), fit overvaluation (8 items), and fit behavioral drive (4 items) was established through exploratory factor analysis. Also, items loading highly on each of the factors had good interitem correlations. In Study 2 (N = 354, age 16-63), women completed the 20-item FIIT and validation measures. The 3-factor structure of the FIIT was confirmed, and findings supported convergent, discriminant, and incremental validity of the FIIT subscale scores (and a total score). In Study 3 (N = 67, age 17-50), the 2-week test-retest reliability of the FIIT scores was high. Overall, the 3 FIIT subscales are related but also distinct domains of fit ideal internalization that conform to theory and may be used as individual subscales or potentially as a composite score.