['There is an increased incidence of breast cancer occurring during pregnancy. Controversy exists as to the safety of performing lymphoscintigraphy during pregnancy and no studies have reported the measured dose of uterine radiation.', 'We performed an institutional review board (IRB)-approved prospective study of uterine radiation resulting from lymphoscintigraphy. Abdominal, perineal, and urinary radiation was measured in 14 breast cancer patients and total uterine dose was calculated.', 'The average dose of 99m-Tc sulfur colloid was 39 +/- 20 MBq (1.04 +/- 0.53 mCi). Measured abdominal and pelvic radiation exposure demonstrated no correlation with patient age or body mass index. The average abdominal radiation exposure was 1.17 +/- 0.87 microGy. The average perineal radiation exposure was 0.23 +/- 0.17 microGy. The average dose to the uterus from bladder radioactivity determined from voided urine was 0.44 +/- 0.44 microGy. The average radiation dose to the uterus (average of abdominal and perineal doses plus contribution from bladder dose) was 1.14 +/- 0.76 microGy. One patient was 16 weeks pregnant at the time of sentinel lymph node biopsy (SLNB) and total calculated uterine dose was 1.67 microGy, suggesting that pregnancy does not significantly alter measured uterine radiation. These data were compared with the average background radiation, which is 3,000 microGy per year or 8.2 microGy per day.'] Does measurement of uterine radiation exposure from lymphoscintigraphy indicate safety of sentinel lymph node biopsy during pregnancy?