We reviewed all known published reports or studies related to a possible cancer-causing or growth-enhancing effect by hyperbaric oxygen. Published articles were retrieved using Medline searches for the period 1960-1993. Additional references were obtained from bibliographies included in those articles discovered in the computer search. Also, hyperbaric medicine text books and the published proceedings of international hyperbaric conferences were visually searched. Studies and reports discovered in this fashion and related to the topic were included in the review. Twenty-four references were found: 12 were clinical reports, 11 were animal studies, and 1 reported both an animal study and a clinical report. Three clinical reports suggested a positive cancer growth enhancement, whereas 10 clinical reports showed no cancer growth enhancement. Two animal studies suggested a positive cancer-enhancing effect, and 10 animal studies showed no such effect. (The report that included both animals and humans is counted in both groups). The vast majority of published reports show no cancer growth enhancement by HBO exposure. Those studies that do show growth enhancement are refuted by larger subsequent studies, are mixed studies, or are highly anecdotal. A review of published information fails to support a cancer-causing or growth-enhancing effect by HBO.