Large and increasing proportions of women work late into pregnancy and resume work soon after delivery. If work in those periods injures their health or that of their infants, this trend would be of public health concern. Data on ever-married primaparas from the National Survey of Family Growth conducted by the National Center for Health Statistics were used to investigate the relationship between working in the last trimester of pregnancy and two indicators of illness--hospitalization of women for complications of pregnancy and hospitalization of their infants during the first year of life. Hospitalization of the mother or child occurred for 15.0 percent of the primaparas. For primaparas who worked in the last trimester of pregnancy, the percentage was slightly higher--17.1 percent. In two groups, black women and women without hospital insurance for delivery, the percentage of mothers or infants hospitalized was much higher among the mothers who worked in the third trimester than among those who did not. The association of working late in pregnancy with higher rates of hospitalization does not mean, necessarily, that working is a cause of hospitalization. It does indicate, however, the need for epidemiologic and medical research on the relationship.