As employers respond to new competitive pressures of global capitalism through layoffs and the casualization of labor, job insecurity affects a growing number of workers. It appears to harm mental health, but less is known about its effects on physical health and health behaviors and the mechanisms through which it may act. The prevailing individual-centered conceptualization of job insecurity as the perception of a threat to job continuity precludes systematic investigation of the social patterning of its health effects. Analysis of data from a 1994 Canadian national probability sample of adults determined that high levels of job insecurity lowered self-rated health and increased distress and the use of medications, but had no impact on heavy drinking. The findings support one possible mechanism of action whereby job insecurity reduces feelings of control over one's environment and opportunities for positive self-evaluation; these psychological experiences, in turn, have deleterious health consequences. There is little evidence of social patterning of this relationship by gender, education, household income, age, marital status, and social support at work.