Background Little is known about frailty in institutionalized older adults, and there are few longitudinal studies on this topic. Objectives To determine the prevalence and attributes of frailty in institutionalized Spanish older adults. Design Cross-sectional analysis of basal data of a concurrent cohort study. Setting Two nursing homes, Vasco Núñez de Balboa and Paseo de la Cuba, in Albacete, Spain. Participants 331 institutionalized adults older than 65 years. Measurements Frailty was defined by the presence of 3 or more Fried criteria and prefrailty by the presence of 1 or 2: unintentional weight loss, low energy, exhaustion, slowness, and low physical activity. Covariables were sociodemographic, anthropometric, functional, cognitive, affective and of comorbidity. Hospitalization, emergency visits and falls in the 6 previous months was recorded. Differences between non-frail and prefrail as one group and frail participants were analyzed using χ 2 tests, t-Student and logistic regression. Results Mean age 84.1 (SD 6.7), with 209 (65.1%) women. 68.8% were frail, 28.4% pre-frail, 2.8% non-frail, and in 2.2% three criteria were not available to determine frailty status. Women were more frequently frail than men (77.1% vs. 22.9%; p <0.001), and frail participants were older (85.1 vs. 82.3; p <0.001) than non-frail ones. Female sex (OR 2.7 95%CI 1.2–6.2), Barthel index (OR 2.2 95%CI 1.2–4.4), depression risk (OR 2.2 95%CI 1.0–4.9) and Short Physical Performance Battery scores (0.7 95%CI 0.6–0.8) were independently associated with frailty status. Frailty had a non-significant association with hospitalization (OR 1.9 95%CI 0.8–4.5) and emergency visits (OR 1.5 95%CI 0.7–3.2) in the previous 6 months. Conclusion In a cohort of institutionalized older adults the prevalence of frailty was 68.8% and was associated with adverse health geriatric outcomes.