This study was designed to determine frequency of child safety seat use for children under the age of 4 years in Michigan, as well as to determine types of misuse. No state has previously conducted such a statewide survey. A two-stage sampling plan was used with data collected through direct observation at a sample of 88 child-care centers and pediatric clinics throughout the state. Misuse data were collected at a subset of the sites through driver interview and visual and hands-on inspection. The study results indicate that 74.5% of children under 4 years of age in Michigan are in safety seats with use highest in vehicles driven by belted drivers, females, and drivers under 60 years of age. Some degree of seat misuse was found in 88.5% of the inspections. The most common types of misuse were related to snugness of fit (both in installing the seat into the vehicle and in securing the child), use of the safety belt locking clip, and the harness positioning clip. Drivers who had a high occurrence of misuse, as compared with drivers with lower misuse, had lower educational levels, removed the seat frequently from their vehicle, were not the parent of the child, and had children who were both younger and smaller. The results show that efforts to encourage people to use child safety seats have been successful.