Diclofenac sodium, a nonsteroidal antiinflammatory drug, is used as an analgesic. However, its effects on pregnant women are not well known. In our study this drug was administered to pregnant rats for a 15-day period. The effects of diclofenac sodium were investigated on umbilical cord vessel diameter, fetal weight and placental weight. It did not affect the diameter of umbilical cord vessels but it significantly increased the umbilical cord length, fetal weight and placental weight (p < 0.05). The results presented here showed that diclofenac sodium should be investigated in the management of growth-retarded fetuses.