Although the current smoking prevalence among Hispanics/Latinxs (10%) is lower than in non-Hispanic whites (15%), higher prevalence is observed among certain subgroups (e.g., Puerto Rican males, 19%). Hispanic/Latinx smokers face unique challenges such as lower awareness and acceptability of nicotine replacement aids, lower prevalence of using counseling or medication, and receiving less advice to quit by their health care providers. Despite these barriers to smoking cessation, few interventions specifically targeted to Hispanic/Latinx smokers have been developed and evaluated. This paper summarizes the design, methods, analysis plan, and sample baseline characteristics of an ongoing randomized controlled trial to assess the efficacy of a Spanish-language self-help smoking cessation intervention among Hispanics/Latinxs. Current smokers who prefer health education materials in Spanish were randomized to one of two conditions. The usual care group received a standard smoking cessation booklet developed by the National Cancer Institute. The intervention group received 10 booklets, 9 pamphlets and a booklet for family and friends mailed monthly over 18 months. All participants complete self-report surveys every 6 months over 2 years. Smoking abstinence is biochemically verified at 12- and 24-month follow-up. A total of 2387 smokers were screened, 2056 were eligible and 1417 were enrolled in the study. The primary outcome is self-reported 7-day point prevalence abstinence. If the intervention is deemed efficacious, it has potential to have a large public health impact with respect to reducing smoking rates and smoking related morbidity and mortality among a large underserved minority population.