To determine whether psychosocial work characteristics are associated with the prevalence of masked hypertension in a population of white collar workers.White-collar workers were recruited from three public organizations. Blood pressure (BP) was measured at the workplace for manual measurements (mean of the first three readings taken by a trained assistant) followed by ambulatory measurements (mean of all subsequent readings taken during the working day). Masked hypertension (MH) was defined as manual BP <140/90 mm Hg, and ambulatory BP ≥135/85 mm Hg. Job strain was evaluated, using the quadrant method for exposure assessment, as well as alternative formulations.BP measurements were obtained from 2,357 workers (80% participation, 61% women; mean age, 44 years). For men, being in the active group (high psychological demands and high decision latitude) was associated with MH (adjusted odds ratio, 2.07; 95% confidence interval, 1.30-3.31). No significant association with a higher prevalence of MH was observed in women.MH is associated with job strain in men. Workers in "active" job situations may be more likely to have the condition.