We evaluated the feasibility, reliability, and validity of a Spanish-language self-administered geriatric assessment (GA) in older (age ≥ 65) Spanish-speaking women with breast cancer in the United States. Eligible participants (n = 181) were recruited and randomized. Feasibility was defined as the participant’s unassisted GA completion rate, completion time, and perception on ease of completion. Reliability and validity were assessed using Spearman’s correlation coefficients. Two-sided p < 0.05 was considered significant. Ninety-eight percent of participants (n = 177) completed the GA at least once. Median age was 70 years (range: 65–95) and 55% had ≤8th grade education. Forty-one percent (n = 73) were unable to complete the GA unassisted, median completion time was 28 min (range 8–90), and 77% (n = 136) rated the GA as “easy”/“very easy”. Patients with ≤8th grade education took longer to complete the GA (30 vs. 25 min, p = 0.0036) and needed more assistance (59% vs. 19%, p < 0.001) than those with ≥9th grade education. Test–retest reliability was high (≥0.82) for all domains except social activity (0.73). Validity among similar scales was found. The self-administered GA is a feasible, reliable, and valid tool for Spanish-speaking older women with breast cancer. Tailoring GA tools to the patients’ educational level is important when implementing tools in multicultural environments.