This paper examines the outdoor thermal comfort in the Mediterranean area. A transversal field survey has been conducted in Rome and, during an entire year, over 1000 questionnaires were filled and combined with micrometeorological measurements. In the first part of the questionnaire, the interviewees answered to personal questions, whereas in the second they evaluated their thermal perception and preference through the ASHRAE 7-point scale and the McIntyre scale respectively. Regression lines were obtained by elaborating the thermal perception votes and determining a PET (Physiological Equivalent Temperature) value for each questionnaire. These regression lines gave the possibility to calculate the neutral PET values: 26.9 °C for the hot season and 24.9 °C for the cold one. Differently, the votes concerning the thermal preference were related to the corresponding PET values through a logistic curve model with the probit function: for the hot season a preferred PET value of 24.8 °C was calculated, whereas for the cold season 22.5 °C. This shows the influence of thermal adaptation. Then since the thermal comfort interval should correspond to the range −0.5÷0.5 of the ASHRAE 7-point scale, a PET comfort range of 21.1÷29.2 °C was obtained. Finally two indexes were determined: the first, called MOCI (Mediterranean Outdoor Comfort Index), is based on the ASHRAE 7-point scale and predicts the mean value of the votes Mediterranean people might give to judge the thermal qualities of an environment; the second is the adaptation of the PPD (Predicted Percentage of Dissatisfied) relation to the Mediterranean population. •A transversal field survey (over 1000 questionnaires) was performed during a whole year.•The neutral PET values are 26.9 and 24.9 °C respectively for hot and cool seasons.•The preferred PET values are 24.8 and 22.5 °C respectively for hot and cool seasons.•The PET comfort range is defined as being 21.1÷29.2 °C.•A new empirical index (MOCI) is proposed and the PPD relation readapted.