Concerns have been raised about the safety of the electromagnetic (microwave) emissions of radars, as well as about the ionizing radiation that is emitted on short distances (<2 m) by devices in the radars producing the microwaves. We retrospectively compared the cause specific mortality of 4,417 Belgian professional male military personnel who served in anti-aircraft radar units in Germany between 1963 and 1994 to the cause specific mortality of 2,932 Belgian military personnel who served at the same time in the same place in battalions not equipped with radars. Mean follow-up was 26 years in the 2 groups. Age-adjusted rate ratio (RR) and 95% confidence intervals were derived from a Poisson regression model. Four hundred twenty-four deaths in the battalions groups and 271 deaths in the control battalions occurred (RR = 1.04 (0.96-1.14)). For specific causes of deaths, RRs were 1.22 (1.03-1.47) for neoplasms and 3.51 (1.19-10.3) for symptoms, signs and ill defined conditions. RRs for other causes of death were not significantly different from 1.00. Among deaths from neoplasms, RR for hemolymphatic cancer was 7.22 (1.09-47.9). RRs for other causes of cancer deaths were not significantly different from 1.00. The results for specific tumor types were all based on very small numbers. The RR for cancer increased with decreasing age and suggested that the RR for cancer increased with the duration of stay in radar battalions. In conclusion, exposure of professional military personnel to anti-aircraft radars that existed in Western Europe from the 1960s until the 1990s may have resulted in an increase in the incidence of hemolymphatic cancers. It remains to be established whether this increase is due to microwaves generated by radars or ionizing radiation produced by electronic devices producing the microwaves.