Angiotensin-converting enzyme inhibitors (ACEIs) are effective antihypertensive drugs, but use of ACEIs during the second and third trimesters of pregnancy has been associated with a pattern of defects known as ACEI fetopathy. The predominant feature of the fetopathy is renal tubular dysplasia. Other associated conditions include hypocalvaria, intrauterine growth retardation (IUGR), and patent ductus arteriosus (PDA). These features may be related to fetal hypotension secondary to ACEI-induced decreases in fetal angiotensin or increased bradykinin. Although no adverse fetal effects have been linked to first trimester use of ACEIs, there has been no systematic evaluation of births to women with such exposures. To determine whether features of ACEI fetopathy occurred after first trimester exposure, in 1992 the Organization of Teratology Information Services (OTIS) in North America initiated the ACEI Registry; two members of the European Network of Teratology Information Services agreed to participate. This report presents findings from the ACEI Registry, which indicate that the infants of 66 women who self-reported first trimester only exposure to ACEI showed no evidence of renal tubular dysplasia.