Critical illness polyneuropathy and myopathy (CIPNM) frequently develops in patients hospitalized in intensive care units. The number of patients with CIPNM admitted to inpatient rehabilitation is increasing. The aim of this study was to comprehensively evaluate the outcome of their rehabilitation. Twenty-seven patients with CIPNM were included in the study. The diagnosis was established clinically and confirmed electrophysiologically. Manual muscle testing was used for the assessment of function. Activity was assessed using the functional independence measure and two walking tests. The patients were also assessed using an adapted International Classification of Functioning, Disability and Health (ICF) checklist. All assessments were performed at admission and discharge. Clinically important and statistically significant improvements were found in all observed measures. High and significant correlations were found between the measures, except between muscle strength and the results of walking tests. Improvement in body functions during rehabilitation decreased as the time from established diagnosis to the start of rehabilitation increased, but it was not related to rehabilitation duration. Improvements in terms of the ICF mainly corresponded to the gain in functional independence measure scores. Major improvement regarding body functions and activities/participation was achieved in patients with CIPNM with a relatively short rehabilitation. Rehabilitation of such patients should start as early as possible once the diagnosis has been established. Comprehensive assessment of such patients combining established scales, objective clinical tests, and the ICF is recommended.