The benefits of continuous positive airway pressure (CPAP) treatment for obstructive sleep apnea are well established, but adherence tends to be low. Research exploring CPAP practitioners' beliefs around determinants of CPAP adherence, and the actions they use in clinical practice to promote CPAP adherence is lacking. This study aimed to: (i) develop and validate a questionnaire to assess beliefs and current practices among CPAP practitioners; (ii) explore practitioners' beliefs regarding the main determinants of patient adherence, and the actions practitioners most commonly use to promote CPAP adherence; and (iii) explore the associations between perceived determinants and adherence-promotion actions. One-hundred and forty-two CPAP practitioners in Sweden and Norway, representing 93% of all Swedish and 62% of all Norwegian CPAP centres, were surveyed via a questionnaire exploring potential determinants (18 items) and adherence-promotion actions (20 items). Confirmatory factor analysis and second-order structural equational modelling were used to identify patterns of beliefs, and potential associations with adherence-promotion actions. Patients' knowledge, motivation and attitudes were perceived by practitioners to be the main determinants of CPAP adherence, and educating patients about effects, management and treatment adjustments were the most common practices. Knowledge was shown to predict educational and informational actions (e.g. education about obstructive sleep apnea and CPAP). Educational and informational actions were associated with medical actions (e.g. treatment adjustment), but knowledge, attitude and support had no association with medical actions. These findings indicate that a wide variety of determinants and actions are considered important, though the only relationship observed between beliefs and actions was found for knowledge and educational and informational actions.