Background: Sleep disturbance and agitation are frequent conditions during the subacute period of recovery in moderate to severe traumatic brain injury (TBI). Clarity is needed regarding the association between the two conditions to improve fundamental nursing care. Aim: The aim of our scoping review was to identify the evidence for potential associations between sleep disturbance and agitation during subacute inpatient rehabilitation of adult patients with moderate to severe TBI. Design: We conducted a five-step scoping review. Methods: Sources of evidence were PubMed, CINAHL, PsycINFO, Cochrane, and Web of Science databases. Eligibility criteria were as follows: English or Scandinavian language articles describing sleep and/or agitation during inpatient rehabilitation of adult patients with moderate to severe TBI and published in the period 2000–2019. Results: We identified 152 articles of which we included six. The included articles were all affiliated with the USA using quantitative methodology. The association between sleep disturbance and agitation is highly complex, with disturbed sleep affecting cognitive and emotional functions. Sleep disturbance was associated with posttraumatic amnesia (PTA)/posttraumatic confusional state, cognitive function, and agitation. Our review suggested a bidirectional association between these symptoms during early TBI rehabilitation. We inferred that improved sleep might be a contributing factor to the resolution of PTA, cognitive impairment, and agitation. Conclusion: The association between sleep disturbance and agitation is still undetermined, but we assume that improved sleep may protect against neuropsychiatric problems in patients with moderate to severe TBI. Larger controlled interventional studies are needed to provide the evidence of modifiable factors for improving sleep during inpatient TBI rehabilitation. Owing to the current lack of publications, it is probably too early to perform a systematic review on the topic. Relevance to clinical practice: We recommend systematic implementation of sleep hygiene during inpatient rehabilitation of patients with TBI to reduce PTA, agitation, and long-term neuropsychiatric problems.