Objectives Comorbidities that are less well known than substance use disorders may occur in individuals experiencing a first-episode psychosis (FEP). This article reviews the importance of these comorbidities through a synthesis of the literature, informed by the authors' clinical experience. Methods Five main groups of comorbidities are discussed: anxiety and obsessive-compulsive disorders, depression, borderline personality disorder, gambling disorder and attention deficit disorder. For each of these disorders, data on their frequency, their impact on the outcome of affected individuals, their detection and treatment will be discussed and interpreted in light of the authors' clinical experience. Results These comorbidities have been relatively neglected by research, even more so in the specific context of FEP. Nevertheless, the data that are available suggest that they are very common in this population. For example, it is estimated that the prevalence of social anxiety disorder may be as high as 50% and obsessive-compulsive disorder 13.6%. The manifestations of these comorbid disorders are sometimes difficult to dissociate from those of the illness; several manifestations of the psychoses can be encountered in these comorbid disorders and vice versa. For example, the social withdrawal sometimes encountered in anxiety disorders or depression may be confused with negative symptoms; behavioural disturbances resulting from delusional beliefs or behavioural disorganization occurring in psychosis may lead to a misdiagnosis of a personality disorder; psychotic symptoms occurring in a personality disorder share characteristics with those occurring in psychotic disorders; cognitive difficulties associated with an attention deficit disorder may give the impression of being directly related to the psychotic disorder. In some cases, antipsychotic treatment may contribute to the emergence of manifestations of these comorbid disorders, for example, obsessive-compulsive disorder occurring on clozapine, or gambling disorder occurring during treatment with a dopamine agonist. While treatments for these comorbidities have been poorly evaluated in the FEP setting, available data and clinical experience suggest that treatments used in other populations, when adapted to the FEP setting, may be effective. Conclusion Overall, there is little literature addressing these comorbid disorders in FEP. Yet, the available evidence suggests that they are common, and that their detection and treatment can support recovery in individuals coping with FEP. Thus, it is essential to consider them from a recovery-oriented early intervention practice perspective.