In addition to making policies, taking decisions and designing activities that ensure availability and accessibility of drugs for the whole population, rationalizing prescription and usage of medicines is another important duty of health authorities. In this regard assessing the rationality of the usage of medicine is of great importance. One of the illustrious methods of such assessment is the WHO guidelines. In this study prescription and drug usage was evaluated in 55 randomly chosen daily and 24 hour service pharmacies in Tehran.The main indicators such as, number of items per prescription, difference between prescribed, dispensed drugs, percentage of antibiotics, injections prescribed, drugs without prescription, existense of essential drugs, dispensing time, over the counter drugs and etc were investigated for five regions of the city of Tehran (north, south, east, west and center) and compared to each other.It was found that the average number of drug items per prescription was 3.60 In daily pharmacies fifty nine percent of patients knew about recommended dosage and number for 24 hour service pharmacies was only 20% about 43% of prescriptions contained at least one antibiotics and 39% at least one injectable item In daily pharmacies, 43% of patients who requested drugs without prescription, received their drugs. The average dispensing time (time of consultation allocated to each patients by pharmacists) was only 35 seconds. Nearly 28% of essential drugs were not available in pharmacies at the time of study.These results show that prescription and drug usage in Tehran do not follow academic practice.