OBJECTIVE: While relationships between working conditions, bullying and health issues have been proven, most studies have investigated these relationships in large enterprises (> 250 employees). Indeed, only a few studies have analyzed this issue in small firms, despite the fact that the latter differ from the former at multiple levels. Therefore, our objective was twofold: to assess whether the size of a firm had an impact on the frequency of workplace bullying and to identify whether the effects of bullying on workers' health differed according to the size of the company. METHOD: Data from the 2010 SUMER French periodical cross-sectional survey were analyzed (N = 31,420 for the present study). Bullying at work was measured based on nine possible hostile attitudes derived from the French version of the Leymann Inventory of Psychological Terror. Two other questions measured colleague-to-colleague verbal violence and sexual or physical assaults. Anxious or depressive episodes were measured using the Hospital Anxiety and Depression scale (HAD). Other health issues were: perceived health status, sickness absence (at least one absence lasting more than eight days), and work injuries. RESULTS: Our findings show that bullying at work was less frequent in micro enterprises (< 10 employees). Anxiety/depression, perceived health status, sickness absence (at least one lasting more than eight days) were significantly associated with workplace bullying, but the effects of bullying were significantly higher in micro enterprises (statistical interaction). CONCLUSION: This study highlights how a firm's size influences workplace bullying and, in particular, the prevalence and consequences of bullying in micro enterprises. The implication and guidelines for practice are discussed.Read less <