212 patients with colorectal cancer will be investigated before surgery and 100 of them after surgery. 597 individuals from a previous population based study will serve as controls to the prevalence of sleep apnea in the general population.

Investigations will include polysomonographic sleep apnea recordings during one night, lung function measurements, blood gas samples and questionnaires.

Controls: Men and women from two population-based cohort studies

Inclusion: 212 patients with colorectal cancer will be investigated before surgery and 100 of them will also be investigated in the same manner after surgery. Due to drop-outs we calculate a need of inviting at least 250 patients.

Controls: 597 individuals from a previous population based study will serve as controls to the prevalence of sleep apnea in the general population.

Exclusion: Dementia, CPAP treated sleep apnea investigations: Patients are investigated with lung function, blood-gas samples, questionnaires, overnight polysomnographic sleep apnea recordings including oro-nasal airflow, thoraco-abdominal respiration belts, chin-EMG, EOG, EEG, ECG (V5) and body position.

Controls: Men and women from two population-based cohort studies the "Sleep and health in women" and the "Men in Uppsala: A Study of Sleep, Apnea and Cardiometabolic Health" and older men and women from a local senior organization.

Outcomes: Prevalence of sleep apnea and hypoxia, sleep quality, and lung function, blood gas, STOP-BANG, Epworth sleepiness scale, Mallampati score, symptoms of sleep apnea, surgical complications, mortality, cancer severity.

Inclusion Criteria:

• Patients scheduled for surgery of colorectal cancer

Exclusion Criteria:

• Dementia, CPAP treatment for obstructive sleep apnea

Patients scheduled for surgery of colorectal cancer Healthy volunteers from population based studies will be included as controls