Ultrasonographic examinations, including placental grading, were done in 145 smoking and 100 nonsmoking low-risk obstetric patients at 37 weeks' gestation. Extensive calcification--grade III changes--occurred significantly more often in smokers than in nonsmokers (36 versus 14%; P less than .0001). Two groups of smokers, consuming five to 15 cigarettes per day or one or more packs per day, also had significant differences in grade III placenta when compared with nonsmokers. Smokers under age 20 years were more likely to have premature grade III changes; however, parity did not influence premature placental calcification in smokers and nonsmokers. The incidence of small for gestational age infants delivered was not significantly higher in smokers, and grade III placental changes appeared to occur no more often in SGA infants of smokers than of nonsmokers. Our findings suggest that the smoking gravida is at increased risk for premature placental calcification.