OBJECTIVE: The objective of the study was to compare levator and obturator thickness between asymptomatic black and white nulliparas using three-dimensional (3D) magnetic resonance imaging (MRI) color mapping. STUDY DESIGN: 3D color-mapped MRI of pelvic muscles were evaluated in 22 similar nulliparas (12 black, 10 white). Levator and obturator (OI) were divided into right and left. Levator was subdivided into puborectalis (PR) and ileococcygeus (IC) portions. Maximal thickness of each muscle was recorded and compared between groups. Nonparametric testing was applied, with significance at P = .05. RESULTS: Levator thickness was significantly greater in blacks bilaterally (median right PR, 8.5 vs 6.0 mm; P = .001; right IC, 6.5 vs 4.5 mm; P = .002; left PR, 9.5 vs 5.75 mm; P = .0002; left IC, 6.5 vs 5.75 mm; P = .02). Obturator thicknesses were similar (right OI, 20.0 vs 19.5 mm; left OI, 19.25 vs 19.25 mm; P = NS). CONCLUSION: Significantly thicker levators but similar obturators were seen in black nulliparas, compared with white nulliparas. These levator differences may influence pelvic floor dysfunction risk. The clinical significance of these findings is under study.