OBJECTIVE: The purpose of this study was to develop a system to quantify interindividual variation in the appearance of continence system structures in normal continent nulliparous women. STUDY DESIGN: Magnetic resonance imaging (1.5 T) was performed in 20 healthy continent nulliparous women (mean age, 30.1 +/- 5.1 years) with normal pelvic organ support and urodynamics. Morphometric measurements of the levator ani muscle, endopelvic fascia, and urethra were performed. RESULTS: The ratio of the maximum-to-minimum measured values shows that 2- to 3-fold differences occur in distance, area, or volume measures of continence system morphologic features. The mean urogenital hiatus area was 15.2 +/- 2.9 cm(2) in women without a visible connection of the levator ani muscle to the pubic bone (4/20 women) and 12.3 +/- 2.4 cm(2) in women with an levator ani muscle-pubic bone connection (16/20 women, P =.05). CONCLUSION: Considerable variation that was not attributable to limitations of the measuring technique that was used occurs in the size and configuration of the urethral support structures in nulliparous asymptomatic women.