Our objective was to compare maternal pelvimetry and patient acceptability between open low-field (0.5-T) and closed 1.5-T MR systems. Thirty women referred for pelvimetry (pregnant: n=15) were scanned twice in the supine position, once in the vertical open system and once in the closed system. Each patient completed a comfort and acceptability questionnaire. Pelvimetric and questionnaire data were compared between systems. Total scan time was double in the open system (7:52+/-1:47 vs 3:12+/-1:20 min). Poor image quality in the open system prevented assessment of interspinous and intertuberous diameters in one woman and all measurements in another, both pregnant, with abdominal circumferences >120 cm. The open system was much more acceptable in terms of claustrophobia and confinement (both p<0.01). Claustrophobia interrupted one closed examination. Thirty-three percent of pregnant women in both systems reported fear of fetal harm. Sixty percent of all women preferred the open system, 7% the closed system, and 33% had no preference. Limits of agreement of 3-5% from the mean for all diameters confirmed good pelvimetric reproducibility. Women's preference for open-system MR pelvimetry is feasible with abdominal circumferences <or=120 cm.