During pregnancy fundamental changes occur in a woman's body that make physical discomforts almost unavoidable. Extensive literature searches revealed that there was no psychometrically acceptable tool available to assess accurately maternal physical discomfort. This paper presents the procedures undertaken to develop the Maternal Physical Discomfort Scale (MPDS), an assessment instrument designed to quantify the type and number of maternal physical discomforts. The MPDS, a scale consisting of 36 items, was developed and psychometrically evaluated using factor analysis, item response theory and reliability measures. The initial version of the scale was validated by a sample of 307 pregnant women. Based on the result from this sample, the MPDS was modified to 33 items and validated by a further sample of 125 pregnant women. The MPDS developed in this study was demonstrated to have content and construct validity and to be reliable.