A total of 184 infants in a neonatal intensive care unit with birthweights less than 1501 g were rated daily on a Morbidity Scale covering the 20 most common diseases and pathophysiological states in neonatology, the severity of each condition being rated on a scale of 0 to 3. To measure the impact of various degrees of complications on parental caretaking style, 20 infants with serious medical complications were paired with 20 infants who had a comparatively easy medical course. Both groups were observed during maternal visits to the hospital and again during a feeding three months after discharge home. Sick infants showed significantly less motor movements when ill but after recovery were similar to well infants of the same age. Parents visiting sick infants interacted far less with their infants than did parents of well babies, and this continued after recovery. It also persisted at home two months after the expected date of delivery. In addition, mothers whose infants had been seriously ill for less than 17 days interacted with them significantly more than mothers whose babies had been ill for over 35 days. While maternal background variables predicted the level of maternal activity with the comparatively well infants and those with short illnesses, they did not do so in the group of infants with long illnesses.