Also known as obesity hypoventilation syndrome (OHS), this is defined to be alveolar hypoventilation while awake (resulting in hypoxemia and metabolic imbalance) in extremely obese patients. Other symptoms include hypersomnolence, dyspnea and pulmonary edema (from pulmonary hypertension). Patients often have obstructive sleep apnea (OSA) as well, which contributes to the symptoms.

"Pickwickian" refers to a Charles Dickens character (from the book The Posthumous Papers of the Pickwick Club). The symptoms resembled those of a character, Joe, in the book (commonly known as the Pickwick Papers).

Treatment includes noninvasive positive pressure therapy (for both OHS and OSA).