In recent years, the concept of fluctuating or recurring impairments has grown both in the public consciousness as well as in frequency of note within policy documentation and legislation. However, contention still surrounds the perceived legitimacy of such impairments, including chronic fatigue syndrome/myalgic encephalomyelitis, epilepsy and diabetes, which have the potential to vary in intensity over time, versus more "traditional" and accepted forms of disability. By drawing on current conceptual discussion and research activities in Canada around what have been termed episodic disabilities, as well as legislative developments in the United Kingdom, this paper will provide an overview of how fluctuating or recurring impairments have to date been conceptualised, contested, and the central issue of competing definitions within this context.