Background: Currently, 47- 62% of multiple sclerosis (MS) patients complain of intermixed sleep disturbances that have profound impacts on their quality of life. Despite robust evidence for sleep disturbance as a modifiable risk factor in development of cognitive dysfunction, as well evidence that modifying sleep-related behaviours improves insomnia, fatigue and depression in MS, relationship between sleep disturbance and cognitive dysfunction in MS remains understudied. Purpose: This study aimed to investigate the relationship between sleep disorders and cognitive functions in patients with multiple sclerosis. Subjects and Methods: Seventy patients with RRMS with sleep disorders from both sexes were recruited. Their age ranged from 20 to 50 years old and their Expanded Disability Status Scale (EDSS) score ≤ 5. Twenty age and sex matched RRMS without sleep disorders were included as a control group. All participants were submitted to the Arabic version of Pittsburgh Sleep Quality Index (PSQI) and Epworth Sleepiness Scale (ESS) to evaluate sleep disorders. Computer Based Cognitive Assessment (RehaCom system) was also used to evaluate cognitive functions. Results: A highly significant difference was detected between the study and control groups as regard mean scores of PSQI and ESS (P < 0.001) being higher in the study group. The mean score of Figural memory was significantly lower in the study group compared to controls (P= 0.031), also, the mean score of reaction behavior tends to be significantly lower in the study group (P= 0.06). A significant negative correlation was found between scores of PSQI scale and Reaction behavior domain (P= 0.049). No significant correlation was found between scores of PSQI scale and attention and concentration domain (p= 0.841), Figural memory domain (P= 0.150), or Logical reasoning domain (P= 0.721). No significant correlation was detected between scores of ESS and attention and concentration domain, Figural memory domain, Reaction behavior domain, or Logical reasoning domain (P> 0.05). Conclusion: there is a relation between sleep disorders measured by PSQI, figural memory and reaction behavior in patients with remission relapsing MS (RRMS).