Hispanic Americans comprise the largest and fastest-growing ethnic minority in the USA. In Houston, Texas, 44% of the population is of Hispanic descent, with the majority being Mexican Americans (78%). This population is under-represented in health-related research despite their high prevalence of obesity and diabetes, which may predispose them to cancer and other chronic conditions. Recognizing the need for a greater research effort into the health risks of Hispanic Americans, the population-based Mexican American (Mano a Mano) Cohort study was launched in 2001. This is an open cohort with enrolment ongoing to 2019, and as of 30 June 2014, 23 606 adult participants from over 16 600 households were enrolled. Bilingual interviewers elicit information in person on demographics, acculturation, lifestyle, occupation, medical history, family cancer history, self-reported and measured height and weight, and other exposures. Urine, blood and saliva samples have been collected at baseline from 43%, 56% and 63% of participants, respectively. DNA samples are available for about 90% of participants. Incident cancers and other chronic diseases are ascertained through annual telephone re-contact and linkage to the Texas Cancer Registry and/or medical records. Molecular data such as genetic ancestry markers, blood telomere length and HbA1c, a marker of impaired glucose tolerance, are available for a substantial proportion of the participants. Data access is provided on request [manoamano@mdanderson.org]. For further information please visit [www.mano-mano.us].