Background/aim: Multiple asthma guidelines have been developed to reduce asthma mortality, morbidity, and cost associated with asthma worldwide. In Malaysia, within this context, it is relatively unknown to what extent doctors adhere to the asthma guidelines. This study aimed to assess guideline adherence and calculate the cost of adhered and nonadhered prescriptions by medical doctors in a public tertiary health care facility. Materials and methods: A cross-sectional study was carried out at Hospital Pulau Pinang, Malaysia. One hundred and eighty patients, a total of 30 patients per doctor, were enrolled to assess guideline adherence. The patients were followed for a second visit to assess their lung function. The costs of adhered and nonadhered prescriptions were calculated. Results: One hundred and forty-three patients (79%) received guideline (Global Initiative for Asthma 2011)-adhering pharmacotherapy. In the majority of patients (n = 133, 73.9%) asthma control was classified as partially controlled. There was no significant association observed between patient asthma control and patient demographics; however, there was a significant difference (P < 0.001) between lung function values from the first and second visits. The cost of adhered prescription was higher (70.1 Malaysian ringgit) than that of nonadhered prescription (13.74 Malaysian ringgit). Conclusion: Fair levels of guideline adherence were observed. Emphasis should be placed on identifying appropriate cost-effective medication regimens based on patient asthma control and constant feedback from patients.