Based on a database accumulated from several recent surveys of office buildings located in a temperate climate (Denmark), the effect on occupant perceptions and symptom prevalence was compared in buildings with natural and with mechanical ventilation in which earlier studies have shown a discrepancy in the degree of perceived control. The database was composed of 1272 responses obtained in 24 buildings of which 15 had mechanical ventilation (997 responses) and 9 had natural ventilation (275 responses). The number of occupant-reported control opportunities was higher in buildings with natural ventilation. Analysis of occupant responses, after grouping according to categories determined by the degree of satisfaction with the perceived control, showed that it was more likely the degree of control satisfaction that affected the prevalence of adverse perceptions and symptoms. Thus, the degree of control, as perceived by occupants, seemed more important for the prevalence of adverse symptoms and building-related symptoms than the ventilation mode per se. This result indicates that even though the development and application of new indoor environment sensors and HVAC control systems may allow for fully automated IEQ control, such systems should not compromise occupants' perception of having some degree of control of their indoor environment.