Importance: Studies report disproportionate increases in cannabis use among middle-aged (50-64) and older (65+) U.S. adults, groups particularly vulnerable to its adverse effects. However, national data on attitudes towards cannabis use and legalization, as well as prevalences of key cannabis-related behaviors are lacking for these groups. Objective: To present national prevalences of past-year any cannabis use, medical use, consumption methods, and other important use-related behaviors, and attitudes toward use, as well as associations of such behaviors and attitudes to cannabis use among U.S. adults ages 50 and older. Design: Cross-sectional data from the Health and Retirement Study (HRS) were used to calculate weighted prevalences for all cannabis measures by primary age groups (50-64, ≥65) as well as two specified older age groups (65-74, ≥75) and sex. Associations between sociodemographics and cannabis use were evaluated using multivariable logistic regression. Main Outcomes and Measures: Self-reported past-year cannabis use (outcome), consumption methods, medical use and health conditions for which cannabis was used, prescriptions by healthcare providers, current and past perception of acceptability, perceptions of risk, and attitudes toward legalization (exposures). Covariates included sex, race/ethnicity, household income, and employment status. Setting and Participants: HRS participants who completed the 2018 cannabis use experimental module (n=1,324). Results: Past year cannabis use was reported by 18.5% (SE=2.17) and 5.9% (SE=1.19) of middle-age and older adults, respectively in the U.S. In both groups, a majority of individuals consumed cannabis exclusively by smoking. Approximately 25% of middle-aged adults and 20% of older adults used cannabis for medical purposes, with ~20% in both groups receiving a prescription or recommendation for medical use from a healthcare provider. Over 75% of individuals in both age groups viewed medical use of cannabis as acceptable, and older adults were more likely to view cannabis as a gateway drug and to support restrictions of cannabis laws. Conclusions and Relevance: Cannabis use among both middle-aged and older U.S. adults is higher than previously reported in state- and national-level studies, with many engaging in cannabis behaviors associated with increased harm. Greater public health and clinical efforts are needed for tailored prevention and intervention strategies.