BACKGROUND: Hypothyroidism has been associated with increased pulmonary morbidity and overall mortality. We conducted a systematic review to identify the prevalence and underlying mechanisms of respiratory problems among patients with thyroid insufficiency. METHODS: PubMed and EMBASE databases were searched for relevant literature from January 1950 through January 2015 with study eligibility criteria: English-language publications; Adult subclinical or overt hypothyroid patients; Intervention, observational or retrospective studies; and respiratory manifestations. We followed the PRISMA statement and used the Cochrane's risk of bias tool. RESULTS: A total of 1699 papers were screened by two independent authors for relevant titles. Of 109 relevant abstracts, 28 papers underwent full text analyses, of which 22 were included in the review. We identified possible mechanisms explaining respiratory problems at multiple physiological levels such as the ventilator control system, diaphragmatic muscle function, pulmonary gas exchange, goiter caused upper airway obstruction, decreased capacity for energy transduction, and reduced glycolytic activity. Obstructive sleep apnea syndrome was found among 30% of newly diagnosed patients with overt hypothyroidism, and demonstrated reversibility following treatment. The evidence for or against a direct effect on pulmonary function was ambiguous. However, each of the above mentioned areas were only dealt with in a limited number of studies. Therefore, we refrain from giving strong conclusions on any of these themes. Moreover, most studies were hampered by considerable risk of bias due to e.g. small numbers of patients, lack of control groups, randomization and blinding, and differences in BMI, gender, and age between subjects and controls. CONCLUSION: Mechanistic data, linking hypothyroidism and respiratory function are at best limited. This area of research is therefore open for retesting hypotheses, using appropriate study designs and methods. Systematic review registration number on PROSPERO: CRD42015016815.