Background and Objectives: Hemodialysis (HD) is one of the therapeutic modalities patients. Since inadequate dialysis increases mortality and morbidity of patients, therefore, assessment of dialysis adequacy is clinically important. For this reason, hemodialysis adequacy was determined in patients undergoing maintenance HD at the Mostafa Khomeini Hospital, Tehran, Iran. Materials and Methods: The cross-sectional, descriptive, and analytic strategy of this research study was conducted on 54 patients in 2005. All of the patients were consented and informed of the study purposes. Data were collected using a reliable questionnaire including age, gender, height, weight, and dialysis duration. Prescribed, delivered, and equilibrated kt/v and URR (urea reduction ratio) were calculated using urea kinetic modeling formulas. All data analysis was carried out using t-test, Fisher exactly test, and Pearson correlation analysis (SPSS software). Results: The study population consisted of 54 patients undergoing conventional maintenance HD (36 males and 18 females) aged 18-83 years. The mean value of age was 55.27 ± 17.28 years. The mean values of prescribed kt/v, dkt/v (delivered), ekt/v (equilibrated), and URR were 1.11 ± 0.19, 0.94 ± 0.18, 0.8 ± 0.15, and 55.33 ± 7.05 respectively. Based on DOQI guidelines, the percentage of adequate prescribed kt/v, ekt/v, and URR were 33.3 %, 11.1 %, and 11.1 % respectively. The mean value of age in inadequate ekt/v group was greater than adequate ekt/v group, although t- test analysis did not show a statistically significant correlation (p = 0.085). In addition, Fisher exactly test showed a statistically significant correlation between adequate ekt/v and gender (p = 0.013) and also between ekt/v and URR (p<0.001). On the other hand, Chi-square test did not show a statistically significant correlation between ekt/v and underlying cause of ESRD (p = 0.685). Conclusion: It was found out that hemodialysis in this center is inadequate in a great percentage of patients, especially in male ones. Further research study with a larger sample size is suggested to evaluate contributing factors in dialysis adequacy. According to these findings, new treatment strategies may also be necessary.