Helmet use is the best preventive measure available against two wheel motorized vehicle (TWMV) related head injuries. In some countries, however, helmets are used only by a minority of TWMV riders. In collaboration with the Road Traffic Police Department, an inspection survey was undertaken to assess the prevalence and to determine predictors of helmet use. The Greater Athens area, Greece, during July and August 1998. A total of 982 TWMVs were stopped, 349 of which had two riders (36%). All riders were interviewed by staff members of the Centre for Research and Prevention of Injuries among the Young. The average prevalence of helmet use was 20.2%. It ranged from 9.7% on small suburban roads to 50.8% on highways. Prevalence of use was significantly lower during the weekend days and at night. Women were significantly more likely to wear a helmet and, controlling for gender, drivers were significantly more likely to be helmet users. Riders of more powerful TWMVs and passengers, who themselves had a TWMV driving license, were helmet users more frequently. Among non-users, the majority (46%) indicated that "the helmet made them feel uncomfortable", particularly in warm weather, whereas 18% claimed that there was little need for a helmet in low speed riding. A multipronged campaign is urgently needed in Greece to increase the prevalence of helmet use by TWMV riders. The campaign should include not only police enforcement but also initiatives to make helmets more convenient to wear and less expensive.