Background. Studies of children raised in institutions have shown that they are at substantial risk in various domains of functioning, but these studies have not examined the children's developmental change at the very early period of institutionalization. Objective. The main aim of this study was to examine the behavioral development of institutionalized infants between three and nine months of life as a function of their birth circumstances and the nature of their institutional care. Design. General behavioral development was studied in 58 (34 males) infants from two St. Petersburg (Russian Federation) institutions (Baby Homes, BH). The infants were divided into four groups according to 1) their gestational age-full-term children (FCh) of 37-41 weeks gestational age, or preterm children (PCh) of 30-36 weeks gestational age; and 2) the type of institutional care environment-either the typical socio-emotionally depriving, non-intervention Baby Home (NoI BH), or an institution that had undergone a program of training plus structural changes intervention (T+SC BH). All the children were assessed at approximately three and nine months of age with the Battelle Development Inventory (BDI; LINK Associates, 1988). Results. Both the FCh and PCh children from the NoI BH displayed significant declines in their BDI Total scores between three and nine months, whereas only the FCh children in T+SC BH improved over this period of time. In general, the FCh group had higher mean BDI Total developmental quotients (DQs) than the PCh group, and children from the T+SCh BH displayed higher scores than children from the NoI institution. Conclusion. Thus, the current study showed that the impact of spending their early months in an institution on infants' development depends on the gestational age of children and the type of institutional care environment.