The Tasmanian devil (Sarcophilus harrisii) is the largest extant marsupial carnivore. A debilitating facial cancer first detected in 1996 has now spread over most of the Tasmanian devil’s range, causing major population declines in affected populations. We compared population structure, reproductive output and survival at two sites before the disease’s arrival and after its establishment. The disease caused major declines in apparent survival rates, resulting in dramatic changes to population age structure and severe and ongoing population declines in the populations studied. These findings suggest that the disease has caused a dramatic change to this species’ life history, representing a shift towards semelparity with most individuals now having only a single breeding opportunity in their lifetime (in contrast to disease free areas where up to 4 litters are possible in the typical 5-6 year life-span).  We did not detect strong impacts of disease on reproductive parameters in the population as a whole and, in fact, found evidence of reproductive compensation occurring in disease populations. This compensatory response may be important for the future persistence of the devil in the face of this disease but to date has been insufficient to counter the significant decline in survival rates.