Pregnant CD-1 mice were exposed to 2.45 GHz CW radiation for 100 min daily at a range of power densities (3.4–28 mW/cm2). Near-term fetuses were examined for gross external morphologic alterations. Mean live fetal weight per litter decreased significantly with exposure to the highest power density (sham, 0.97 ± 0.15 g; irradiated, 0.89± 0.13 g). There was a significantly increased incidence of cranioschisis in exposed fetuses. An exposure of the dam for 100 min at these power densities did not appear to be significant thermally. Estimates of mean dose rate as determined using twin-well calorimetry ranged from 2.0 to 22.2 mW/g.