Arborists are exposed to many occupational hazards and experience more than three times the overall fatality rate of all U.S. workers. Investigations into fatal incidents lead to a better understanding of industry dangers. However, this knowledge does not extend to how tree workers operate when an injury or fatality does not occur. Current research regarding fatal and nonfatal injuries does not include the accreditation status of the company at which the worker was employed, nor whether certified arborists were on staff. Given the highly skilled nature of the work involved, certification and accreditation might ensure a minimum level of demonstrated safety practices. This study aimed to 1. Determine whether certification and accreditation in the tree care industry are associated with safer workplace behavior, and 2. Identify safety practices that tree workers commonly violate. Tree care companies in southern New England were divided into three categories: accredited, non-accredited with certified arborists on staff, and non-accredited with no certified arborists on staff. A stratified random sample of 63 companies was evaluated in the field by direct observation, assessing workers' adherence to the industry's safety standard, the American National Standards for Arboricultural Operations (ANSI Z133.1-2006). Analysis indicated that, overall, accredited companies and those with certified arborists on staff complied with the Z133.1 Standard more than those without. Although these companies were more compliant, few significant differences emerged, and low overall compliance was found for personal protective equipment and chainsaw and chipper safety. There were low levels of compliance across all types of companies with the basic aspects of safety, including feeding the chipper from the curbside, not drop-starting a chainsaw, and using head, eye, and hearing protection. Implications of findings include possible considerations for improvements on accreditation and certification processes. Further findings address aspects of the Z133.1 Safety Standard that are currently unclear.