This paper addresses thermal comfort conditions in office buildings with rudimentary mixed-mode environments controlled by occupants compared to fully air-conditioning in a humid subtropical climate in Brazil. Occupants from three office buildings with two different environmental control strategies (two with mixed-mode ventilation and one with permanent air-conditioning) assessed their thermal environment via “right-here-right-now” online questionnaires, while indoor climatic measurements were simultaneously carried out in situ. 2688 questionnaires from 617 occupants were collected. The results indicated that air-conditioning in mixed-mode (MM) buildings controlled by occupants was used permanently throughout the year without any season pattern, being specially connected to the peak outdoor air temperature. In addition, there was a strong tendency toward thermal discomfort due to excessive cold in MM buildings at times when air-conditioning mode was under operation, and hot discomfort during the naturally ventilated mode. When compared to fully-air conditioning buildings, there were similarities in terms of occupant thermal sensation and acceptability levels within the same intervals of Standard Effective Temperature (SET). The results obtained in this study could be useful as a framework for future studies, as well as a baseline for a Brazilian thermal comfort standard.