Background. Data on the use and efficacy of complementary and alternative medicine (CAM) in patients with asthma are limited, and there is a lack of studies documenting the use of CAM in patients with chronic obstructive pulmonary disease (COPD) in Turkey. Aim. To determine the prevalence of CAM usage in patients with asthma and COPD and to assess the clinical and demographic factors associated with the use of CAM. Materials and methods. A total of 521 patients (313 with asthma and 208 with COPD) were randomly enrolled into this cross-sectional survey. A face-to-face interview was conducted using a structured questionnaire. Results. One hundred sixty-three patients (52%) with asthma and 70 patients (33%) with COPD were reported to be using some form of CAM (p < 0.001). The most popular modalities were herbal remedies (46% and 28% in the two groups, respectively) and animal products (28% and 5% in the two groups, respectively). CAM-practicing asthma patients were typically younger with longer duration of disease and higher income than the CAM-practicing COPD patients. For the patients, the main source of information on CAM practices was their relatives and friends. Only a small number of the patients consulted with their physicians about CAM. The main reasons to use CAM for patients with asthma and COPD were harmlessness and symptomatic relief, respectively. CAM-related adverse effects and difficulties to obtain CAM were significantly higher in patients with asthma than in patients with COPD. Conclusion. There is a high prevalence of CAM usage in patients with asthma and COPD in Turkey. Hence, becoming familiar with CAM therapy and inquiring about patient practice of CAM as part of the routine medical history will allow the physicians to provide reliable information to their patients on these medical practices.