Aim of our study was to assess the relationship between adherence with antihypertensive drugs and the risk of death in frail versus nonfrail old individuals. Using the database of the Lombardy Region (Italy), we identified 1 283 602 residents aged ≥65 years (mean age 76) who had ≥3 prescriptions of antihypertensive drugs between 2011 and 2012. A nested case-control design was applied, with cases being the cohort members who died during the observation period (7 years). Logistic regression was used to model the association of interest, with adjustment for potential confounders. Adherence was measured by the proportion of the follow-up covered by prescriptions, and the analysis was separately performed in patients with a good, medium, poor, and very poor clinical status, as assessed by a score that has been shown to be a sensitive predictor of death in the Italian population. The 7-year death probability increased from 16% (good) to 64% (very poor) clinical status. Compared with patients with very low adherence with antihypertensive treatment (<25% of follow-up time covered by prescriptions), those with high adherence (>75% of time covered by prescriptions) exhibited a lower risk of all-cause mortality in each group, the difference decreasing progressively (−44%, −43%, −40%, and −33%) from the good to the very poor clinical status. Adherence with antihypertensive drug treatment was also associated with a lower risk of cardiovascular mortality. Adherence with antihypertensive appears to be protective in frail old patients, but the benefit is less marked than in patients with a good clinical status.