We aimed to establish the incidence of Frey's syndrome in patients that have been submitted to partial and total parotidectomy at a cancer-treating hospital in Mexico City and to propose a grading system to determine its severity. The incidence of Frey's syndrome in 77 patients (25 male and 52 female) under oncological follow-up due to parotid tumors was subjectively evaluated through clinical findings and objectively diagnosed through Minor's test. The positive hyperhydrotic areas were recorded and measured on transparent acetates. Numeric values were assigned according to clinical perception of symptomatology by the patients (0 for no perception and 1 for clinical recognition), extent of the affected area (1 if less than 2 cm; 2 if between 2.1 and 4 cm, and 3 if more than 4 cm), intensity and smell of sweat (3 if it was excessive or of unpleasant odor). Results were expressed as mild (if less than 4 points) or severe grades (if 4 or more points). Frey syndrome was objectively diagnosed in 28 patients (36%), although only 17 (22%) recognized to have clinical manifestations of this condition. There were 22 women (79%) and six men (21%). Of these, seventeen (61%) had been subjected to partial and eleven (39%) to total parotidectomy. Adjuvant radiotherapy had been employed in nine cases (32%). The cutaneous affected area in the whole group ranged from 0.7 to 29.8 cm(2) (mean 8.9 cm(2)), with a mean affected surface of 8.7+/-10.8 cm(2) for women and 9.0+/-8.8 cm(2) for men ( p > 0.05). Twelve cases were classified as mild and sixteen as severe. No significant differences were found between patients treated with partial vs. total parotidectomy or between patients treated with or without adjuvant radiotherapy. The incidence of Frey's syndrome in Mexican patients seems to be similar to those reported in other countries; however, the extent of hyperhydrosis is lower when compared to some European studies. Our proposal for evaluating this condition may be a helpful tool in assessing the incidence and severity among the diverse populations and it may be a useful tool to define more precisely the indications for treatment and to evaluate the available therapeutic methods according to the severity of the condition.