Paraiotonchium autumnale (Nickle) (Tylenchida: Iotonchiidae) causes parasitic sterilization in female Musca autumnalis DeGeer (Diptera: Muscidae). In addition to sterilization, P. autumnale causes physiological and behavioural changes within its host. However, there have been no records of reduced host lifespan in this system. Studies were conducted in 2009 and 2010 with wild M. autumnalis collected as larvae from cow dung pats from Browns Valley, California, USA. Field-collected larvae were reared to adulthood and flies of the same eclosion dates were caged together, regardless of whether or not they were parasitized. Dead flies were collected daily, and parasitism status was confirmed by dissection. Due to the very different effects of P. autumnale-parasitism on male versus female face flies, flies were analysed separately by sex. Kaplan-Meier analysis revealed a non-significant difference in longevity between non-parasitized and parasitized flies for female and male flies in 2009. In 2010, however, significant differences (P < 0·05) were found between parasitized and non-parasitized female and male flies. In 2010, the median time to death for non-parasitized female flies was 20 days and 15 days for parasitized females. The 2010 median survival time for non-parasitized male flies was 33 days and 15 days for parasitized males. This is a parasite-mediated cost to the host that has not been recorded previously. Based on our results and results from another published study we suggest that the potential for sterilizing parasites to alter host longevity is condition dependent.