To assess the prevalence and correlates of compliance and noncompliance with hand hygiene guidelines in hospital care. A systematic review of studies published before January 1, 2009, on observed or self-reported compliance rates. Articles on empirical studies written in English and conducted on general patient populations in industrialized countries were included. The results were grouped by type of healthcare worker before and after patient contact. Correlates contributing to compliance were grouped and listed. We included 96 empirical studies, the majority (n = 65) in intensive care units. In general, the study methods were not very robust and often ill reported. We found an overall median compliance rate of 40%. Unadjusted compliance rates were lower in intensive care units (30%-40%) than in other settings (50%-60%), lower among physicians (32%) than among nurses (48%), and before (21%) rather than after (47%) patient contact. The majority of the time, the situations that were associated with a lower compliance rate were those with a high activity level and/or those in which a physician was involved. The majority of the time, the situations that were associated with a higher compliance rate were those having to do with dirty tasks, the introduction of alcohol-based hand rub or gel, performance feedback, and accessibility of materials. A minority of studies (n = 12) have investigated the behavioral determinants of hand hygiene, of which only 7 report the use of a theoretical framework with inconclusive results. Noncompliance with hand hygiene guidelines is a universal problem, which calls for standardized measures for research and monitoring. Theoretical models from the behavioral sciences should be used internationally and should be adapted to better explain the complexities of hand hygiene.