Recent study into body dysmorphic disorder (BDD) has raised questions about the validity of its current diagnostic classification as well as categorical division into `psychotic' and `non-psychotic' variants. Furthermore, though individuals with the disorder are believed to experience cognitive difficulties, the precise nature of these deficits remains unclear. This paper aims to provide a comprehensive review of existing knowledge of BDD in terms of its nosology and cognitive deficits. We evaluate arguments in relation to its inclusion within the obsessive-compulsive spectrum disorders (OCSDs), consider how delusionality is coded in BDD, and also examine recent studies suggesting which specific cognitive deficits may underpin the disorder. There appears to be a sound rationale for considering BDD as part of the OCSDs, though current findings indicate that it is not simply a subtype of obsessive-compulsive disorder (OCD). Evidence also suggests that the degree of delusional beliefs in BDD would be more appropriately theorised on a dimensional basis. In terms of cognitive deficits, research to date has implied that attentional biases and/or abnormalities in basic visual processing may be especially important. Further research is needed to elucidate an inclusive profile of the underlying cognitive deficits in BDD. In turn, these insights could help to clarify current nosological debates surrounding the disorder.