Controversy exists whether patients who are genetically heterozygous for 1-antitrypsin deficiency (1ATD), carrying a single PI*Z allele, are at increased risk of developing chronic liver disease. In these investigations, we determined the prevalence of heterozygous 1AT phenotypes (PI MZ, PI SZ) in a well-characterized cohort of patients presenting with chronic liver failure before orthotopic liver transplantation (OLT). We analyzed data collected from all adult patients (n = 641) who underwent OLT at our tertiary referral center between March 1985 and December 1996. Study patients entered a prospective protocol designed to test for all known etiologies of liver disease. Complete testing including 1AT phenotyping was successfully performed in 599 adults. We compared the overall number of heterozygous PI*Z carriers in our OLT cohort with established prevalence figures for general and regional American populations, and examined their distribution among various liver disease subgroups. Fifty-one patients were found to be heterozygous carriers of a single PI*Z allele for 1AT. The predominant phenotype in our transplantation cohort was PI MZ, identified in 49 patients (8.2%), which is a significantly higher prevalence than that reported from previous American population studies (2%-4%). Additionally, a significantly greater number of PI MZ carriers existed in patients with cryptogenic cirrhosis compared with other liver disease categories (26.9%; P < .001). These data suggest that individuals carrying a single PI*Z allele for 1AT may be at increased risk of developing cirrhosis and liver failure, even in the absence of an identifiable coexisting liver disease.