Clinical measurement of pelvic floor muscle activity commonly involves techniques that are both physically and psychologically invasive. This study investigated transabdominal application of ultrasound to measure pelvic floor muscle action. The specific aims were to establish the face validity of ultrasound measures of displacement of the posterior bladder wall as a reflection of pelvic floor muscle contraction, and the reliability of measurement between raters and between testing occasions. Non-pregnant adult female subjects aged 24 to 57 years were tested in lying with a 3.5 MHz 35 mm curved array ultrasound transducer over the lower abdomen. Posterior bladder wall displacement was observed in both sagittal and transverse planes. Digital vaginal palpation and transabdominal ultrasound were undertaken simultaneously during pelvic floor muscle contractions to confirm that pelvic floor contractions were performed correctly and to grade pelvic floor muscle strength. Displacement (mm) was measured using electronic calipers on the ultrasound monitor screen. In all subjects, a correct pelvic floor muscle contraction was confirmed on digital palpation, and consistent anterior and cephalic movement was observed on screen. Digital strength grading did not correlate with ultrasound measures in either transverse or sagittal planes (r = 0.21 and -0.13). Average intra-class correlation coefficients for within session inter-rater reliability ranged between 0.86 and 0.88 (95% CI 0.68 to 0.97), and for inter session intra-rater reliability between 0.81 and 0.89 (95% CI 0.51 to 0.96). Transabdominal application of diagnostic ultrasound is a personally non-invasive method for imaging and assessing pelvic floor muscle activity and is both valid and reliable.