Study objective Although safety belt legislation exists for drivers in Massachusetts, there is an exemption for taxicab drivers. According to the most recent data from the Governor's Highway Safety Bureau, the observed safety belt use rate of drivers in Massachusetts is 64%. However, the safety belt use among taxicab drivers in Boston is unknown. Methods An observational study was conducted to assess the prevalence of safety belt use among taxicab drivers in Boston. We compared our findings with state-level data obtained from the Governor's Highway Safety Bureau. Research staff made observations of taxicabs arriving at various sites within Boston (Logan Airport, Back Bay subway entrance, Government Center, and a hospital in Boston). The methodology used in this study was adapted from MASS-Safe, the Traffic Safety Research Program of the Governor's Highway Safety Bureau. In brief, research staff assessed the use of shoulder safety belts worn by taxicab drivers in Boston. Researchers observed traffic flow coming from a single direction at each observation site. These observers were instructed to include only taxicabs in motion, approaching in the nearest lane to the sidewalk. Results Two hundred fifty taxicabs were observed during the study period. Of these, 247 taxicab drivers were men (98.9%), whereas 3 were women (1.2%). Overall, 17 of 250 taxicab drivers (6.8%; 95% confidence interval 3.9% to 9.7%) wore safety belts, whereas 233 (93.2%) did not. Conclusion The safety belt use among taxicab drivers in Boston is 6.8%, markedly lower than the state-level safety belt use of other drivers in Massachusetts. Stronger safety belt use legislation in Massachusetts may help to improve safety belt use among taxi drivers in Boston.