This study summarizes and reviews the available health information on ortho-phthalaldehyde (OPA), a recently introduced and widespread disinfectant for heat-sensitive medical equipment, particularly focusing on its possible immunological effects in the healthcare setting. OPA properties derived from laboratory and clinical studies, and in vivo and in vitro tests for the diagnosis of OPA allergy are described. The available evidence suggests the spreading of OPA as disinfectant in endoscopy units despite the little available scientific evidence on its safety. Indeed, some papers reported on serious adverse reactions to OPA in patients and, to a lesser extent, in exposed workers, and in vivo studies suggested that OPA is a dermal and respiratory sensitizer. Finally, until more definite safety data become available only suggestions on possible preventive measures can be provided.