In response to a 1991 anencephaly cluster in Cameron County, Texas, a surveillance and neural tube defect (NTD) recurrence prevention project for NTDs was implemented in the 14 Texas-Mexico border counties. For 1993-1995, NTD-affected pregnancies were identified at all gestational ages through active surveillance of multiple case-ascertainment sources. There were 87 cases of anencephaly, 96 cases of spina bifida, and 14 cases of encephalocele for respective rates of 6.4, 7.1, and 1.1 per 10,000 live births. Of the 197 NTD case-women, 93% were Hispanic. The overall, Hispanic, and Anglo NTD rates were, respectively, 14.6, 14.9, and 10.6 per 10,000 live births. The NTD rate for El Paso County (9.8 per 10,000), the most northwestern Texas county, was significantly lower (p = 0.001) than the aggregate rate for the rest of the Texas border (17.1 per 10,000). The overall Texas border rate was significantly higher (p < 0.001) than a recently estimated rate of 9.3 for California and minimally higher than a recently adjusted rate of 11.3 for the Metropolitan Atlanta Congenital Defects Program counties (p = 0.052), both of which now reflect all gestational ages. Of the 197 Texas border cases, 85% (168 cases) reached a gestational age of > or =20 weeks. Excluding cases of <20 weeks' gestation in the rate had a more marked effect on reducing the anencephaly rate (4.9 per 10,000) than the spina bifida rate (6.7 per 10,000). A country of birth was known for 153 (83%) of the 184 Hispanic case-women: 63% were born in Mexico; 24%, in Texas; and 11%, elsewhere in the United States. Rates for Mexico-born Hispanic women (15.1 per 10,000) were significantly higher than rates for United States-born Hispanic women (9.5 per 10,000) (p = 0.006).