OBJECTIVE: Whole body air-displacement plethysmography (BOD POD), a new body composition technique, was validated against hydrodensitometry (UWW) in 67 women wearing a one-piece swimsuit (OP) who represent a wide range of body fatness and age. Additionally, the effect of trapped isothermic air in clothing while in the BOD POD was examined by comparing different clothing schemes (a one-piece swimsuit (OP), two-piece swimsuit (TP), a hospital gown (HG), and a hospital gown previously included in a volume calibration (GC)) in a subset of 25 women. DESIGN: Cross-sectional data analysis. SUBJECTS: 67 healthy Caucasian females. MEASUREMENTS: Body density g/cm3 (Db) by BOD POD and UWW. RESULTS: In 67 females UWW Db (1.030 ± 0.020 g/cm3) was higher (P < 0.01) than BOD POD Db (1.028 ± 0.020 g/cm3). This is a difference of 1.0% fat. The R2 was 0.94, SEE was 0.005 g/cm3 and the regression between Db by UWW and BOD POB did not significantly deviate from the line of identity. In the subset group of 25 subjects, OP Db (1.040 ± 0.014 g/cm3) and TP Db (1.040 ± 0.014 g/cm3) were significantly lower (P < 0.01) than UWW Db (1.044 ± 0.014 g/cm3) or a difference of 1.9% fat. The R2 was 0.86 and the SEE was 0.005 g/cm3 and the regression between Db by UWW and both OP and TP did not significantly deviate from the line of identity. HG Db (1.056 ± 0.016 g/cm3) and GC Db (1.037 ± 0.016 g/cm3) were significantly different (P < 0.01) from UWW Db (1.044 ± 0.014 g/cm3). This difference in density translates to a difference of 5.5% and 3.2% fat respectively. The regression between Db by UWW and both HG and GC significantly deviated from the line of identity. CONCLUSION: This study supports the use of the BOD POD as a substitute for UWW. However, caution should be made in using the BOD POD if subjects are clothed in anything other than a tight fitting swimsuit.