Stuffed mussel is a traditional food, sold by street vendors in coastal parts of Turkey and other Mediterranean countries. In the present study, the microbiological quality of not only the stuffing mixture, but also the outer surface of the stuffed mussels was evaluated for 1 year, and the effect of the ambient temperatures on the prevalence and the count levels of the microorganisms were evaluated. Fifty samples (750 stuffed mussels in total) were collected periodically, and microbiological analyses were performed by standard procedures for aerobic plate count, coliforms, fecal coliforms, Enterobacteriaceae, Staphylococcus aureus, Bacillus cereus, and Vibrio spp. Aerobic plate counts above 5 log CFU/g were obtained in 16 and 72% of stuffing mixture samples at high and low ambient temperatures, respectively, and average aerobic plate counts of outer surface samples at high and low ambient temperatures were 3.21 and 4.34 log CFU/ml, respectively. The prevalence and the count levels of coliforms, fecal coliforms, Enterobacteriaceae, and Vibrio spp. (except for the prevalence of Vibrio spp. in stuffing mixture samples) in the samples at high ambient temperatures were considerably higher compared with those at low ambient temperatures (P < 0.05). High frequencies of pathogens S. aureus and B. cereus were found in stuffing mixture samples at high ambient temperatures, with averages of 2.84 and 2.94 log CFU/g, respectively (P < 0.05). The result of this investigation indicates that stuffed mussels as a street food may constitute a potential health hazard, especially at high ambient temperatures, depending on contamination level and lack of sanitary practices, and therefore, handling practices should require more attention and improvement.