Hydroperiod strongly influences the breeding period and development time of many amphibians, and larvae of various species display developmental plasticity in response to habitat drying. Hydrologic alterations associated with anthropogenic activities potentially can influence host—parasite interactions in humans and wildlife, but few investigators have examined this possibility. Pathogens can delay amphibian development, so infections could constrain the ability of parasitized larvae to respond to a shortened hydroperiod under drying conditions. We examined the individual and joint effects of hydroperiod and infection with a pathogenic trematode parasite (Ribeiroia ondatrae) on larval development of Pacific chorus frogs (Pseudacris regilla) in mesocosms. Tadpoles subjected to accelerated drying were twice as likely to emerge early. However, this tendency was most pronounced among uninfected individuals (96% of early-emerging individuals) and may have arisen from differences in competitive ability between infected and uninfected conspecifics in mesocosms. Our findings indicate the importance of investigating hydrologic variables associated with environmental perturbations, such as climate change, particularly as they relate to the ability of organisms to respond to multiple stressors that include diseases.