A study of proportionate mortality among unionized construction operating engineers was conducted. The study population consisted of 15,843 deceased males who had been active members of the International Union of Operating Engineers for at least 1 year and who died in the United States between January 1, 1988 and December 31, 1993. Death certificates were obtained to determine the causes of death. Proportionate mortality ratios (PMRs) and proportionate cancer mortality ratios (PCMRs) were computed using the corresponding rates among the general male population as the reference. Mortality from all cancers, benign and unspecified neoplasms, emphysema, pneumoconioses, injuries other than from transportation and falls, and suicide was significantly increased, PMRs 1.11, 1.37, 1.43, 1.11, 1.43, and 1.22, respectively. The increase in all cancer mortality was due to increases in the number of deaths from lung cancer, bone cancer, leukemia and aleukemia, and cancer of other and unspecified sites, PMRs 1.26, 2.39, 1.19, and 1.15, respectively. Mortality from blood disorders, mental problems, nervous system disorders, heart diseases, pneumonia, and fall injuries was significantly decreased. The PCMR approach indicated that deaths from all respiratory cancers and bone cancer were significantly increased, PCMRs 1.13 and 2.14, respectively. The significant increase in respiratory cancer mortality was due to a significant increase in mortality from lung cancer, PCMR 1.07. The PCMR for leukemia and aleukemia was nonsignificantly increased. Mortality from buccal cavity and pharynx, digestive system, and thyroid tumors was significantly decreased, PCMRs 0.77 to 0.90. The authors conclude that results appear to confirm earlier findings of an increased risk of death from lung cancer among operating engineers. The causes of the excess deaths from bone cancer and leukemia and aleukemia are unknown. The study results underscore the need to control airborne exposures of construction operating engineers to lung carcinogens.