Self-reports are commonly used tools for obtaining sedentary behaviors. The aim of our study was to assess agreement between two self-reports of sedentary time and a gold standard sedentary time objective monitor. A worksite sample (n = 42) completed the Slovenian version of the Global Physical Activity Questionnaire (GPAQ), the Slovenian version of the Sedentary Behaviour Questionnaire (SBQ for weekdays) and wore an objective physical activity monitor (activPAL) for up to five consecutive working days. Results revealed that GPAQ and SBQ consistently underestimated the total sedentary time, with the mean bias of -165 min/day and -181 min/day, respectably. Wide limits of agreement showed poor precision and intraclass correlation revealed a low level of agreement. GPAQ and SBQ are not recommended to be used in studies seeking for relationships with health outcomes, nor in studies where detecting the behavioral change is of interest. Objective measurement should be the preferred choice when possible.