In the OPPS we have been studying the effects of marihuana used during pregnancy since 1978. The subjects are primarily middle-class, low risk women who entered the study early in their pregnancy. Extensive demographic and life-style information was gathered several times during pregnancy and postnatally. The offspring have been assessed repeatedly during the neonatal period, at least annually until the age of 6 and less frequently thereafter. The outcome measures include a variety of age appropriate standardized global measures as well as a large battery of neuropsychological tests attempting to assess discrete functioning within particular domains including language development, memory, visual/perceptual functioning, components of reading and sustained attention. The results suggest that in the neonate, state alterations and altered visual responsiveness may be associated with in utero exposure to marihuana. Global measures, particularly between the ages of 1 and 3 years, did not reveal an association with prenatal marihuana exposure. However, this initial, apparent absence of effect during early childhood should not be interpreted as in utero marihuana exposure having only transient effects for, as the children became older, aspects of neuropsychological functioning did discriminate between marihuana and control children. Domains associated with prenatal marihuana exposure at four years of age and older included increased behavioral problems and decreased performance on visual perceptual tasks, language comprehension, sustained attention and memory. The nature and the timing of the appearance of these deficits is congruent with the notion of prenatal marihuana exposure affecting 'executive functioning'--goal directed behavior that includes planning, organized search, and impulse control. Such an interpretation would be consistent with the extant literature with animals and non-pregnant adult users suggesting that chronic marihuana use may impact upon prefrontal lobe functioning.