Aim To evaluate the consistency of adherence information given to clinicians by patients with obstructive lung disease and their relatives. Methods A cross-sectional study was conducted in patients with asthma and chronic obstructive pulmonary disease (COPD). Patients and their relatives were independently questioned about the patients’ adherence to inhaler therapy. The consistency of the information given by the patients and their relatives in terms of patient’s adherence to the inhaler treatment was evaluated. Results Sixty-six patients, 42 followed up with a diagnosis of COPD, 24 with a diagnosis of asthma were included in the study. According to the patients’ own statements, the number of patients who regularly used the prescribed inhaler treatment was 59 (89.4%) while 7 (10.6%) patients reported that they used their inhalers irregularly. There was no statistically significant difference in terms of age, gender, education level, smoking, diagnosis, and duration of disease between adherents and non-adherents according to the patient’s own statement. According to the statements of their relatives, 17 (28.8%) of 59 patients who stated that they used the prescribed inhaler treatment regularly used their treatment irregularly. Conclusion The discrepancy determined between the statements given by the patients and their relatives about the adherence of the patients in our study revealed a serious problem in the assessment of adherence according to the patients’ statement. In this context, an approach that includes patient relatives in the assessment of adherence to inhaler therapy may help to evaluate adherence more accurately and to increase patient adherence.