BACKGROUND: The functional decline that follows hospitalization may be especially important in frail populations such as nonagenarians. The present study examined the functional decline among nonagenarians admitted because of exacerbations of chronic obstructive pulmonary disease (COPD) or congestive heart failure (CHF). METHODS: A prospective cohort study was performed on two groups of patients who were distinguished by diagnosis in two tertiary academic medical hospitals. Sixty nonagenarian patients, admitted because of exacerbation of COPD (n=30) or CHF (n=30), were evaluated at admission, upon discharge, and 3 months post-hospitalization. The Barthel Index (BI) was used to assess functionality. The outcome we were interested in was functional decline 3 months after hospital discharge. RESULTS: The inpatient mortality rate was 10%. Overall functional status at discharge, as compared with that before admission, declined in all 54 surviving patients (p<0.001). At the 3-month follow-up, 37 patients were evaluated; a decline in their BI persisted in 60% of them. We did not find significant differences, either upon discharge or at 3 months post-hospitalization, in the decrease in BI rate between COPD patients and CHF patients. CONCLUSIONS: The fact that the underlying disease does not induce differences in the functional outcome of nonagenarians reinforces the importance of using a comprehensive approach at admission and after discharge for all frail patients.