Workers involved in the nuclear fuel cycle have a potential for internal exposure to uranium. The present review of epidemiological studies of these workers aims to elucidate the relationship between occupational internal uranium exposure and cancer risk. Eighteen cohort and 5 nested case-control studies published since 1980 are reviewed. Workers occupationally exposed to uranium appear to be at increased risk of mortality from neoplasms of the lung, larynx, and lymphatic and haematopoietic tissue. Currently available evidence for a positive association between internal exposure to uranium and the risk of cancer is limited. The common weaknesses in reviewed studies include low statistical power and inaccurate assessment of internal exposure to uranium. Further investigations should focus on precise assessment of occupational exposure and address the issue of potential confounders.