The Hispanic population has become the largest ethnic minority group in the United States. To successfully incorporate this population in adult vocational training, social service, and health programs, it is essential that programs design and implement materials at a reading level appropriate for the population served. This study determines the reading level in a population of Hispanic adult substance users receiving HIV prevention services in Long Beach, California. One hundred seven Spanish speakers were administered the Spanish Reading Comprehension Test. Spanish reading ability was determined to be at the third grade level for this sample. Results suggest that substance-using subpopulations of Spanish speakers in the Southwest United States face considerable language and literacy barriers. Findings have implications for adult vocational training as well as social service and health programs that include Hispanic subpopulations, and highlight the importance of designing materials that do not exceed the reading abilities of target populations