Objective: To test Self-Determination Theory (SDT) and examine whether employee perceptions of the workplace physical activity (PA) culture have statistically significant effects on PA behaviour and attitudes, as mediated by the three basic psychological needs. Design: Cross-sectional survey. Setting: Furniture manufacturer in the Midwest, USA. Method: Full-time employees with access to PA resources and facilities at work were surveyed (N = 546; age range = 18-65) on the following measures--demographics, independent variables (PA need supportiveness of work environment, PA norms, social support for PA, employer value of PA and importance of PA), dependent variables (PA at work, PA leisure and PA attitudes) and mediators (psychological need satisfaction in PA for autonomy, competence and relatedness). Standard univariate statistics described the study population. Structural equation modelling (SEM) assessed the associations between independent, dependent and mediator variables. Results: Results from this study indicate PA and attitude towards PA are influenced by perceptions of the environment and various aspects of workplace culture. Statistically significant paths were found within the SEM model between attitude and social support, injunctive norms and PA value; PA done at work and autonomy need satisfaction, competence need satisfaction and descriptive norms; and PA done in leisure time and PA value. Conclusion: In the sample surveyed, work PA culture influences PA behaviour and attitudes. Different aspects of work PA culture influence PA performed at work compared to PA in leisure time.