Purpose Cancer-associated venous thromboembolism (VTE) can cause many unfavorable health outcomes. Many institutions have published guidelines, but implementation of these guidelines in cancer clinics is still under investigation. This study aimed to evaluate the guideline adherence and identify potential gaps between the recommendations and their implications in clinics. Methods A prospective study was conducted between September and December 2018 at oncology inpatient and ambulatory settings. The guideline adherence rate was assessed for inpatients during hospital stay by using 8 criteria developed based on the National Comprehensive Cancer Network (NCCN) Guideline on Cancer Associated Venous Thromboembolic Disease Version 1.2018. Guideline-based recommendations were proposed to the consultant physician in case of non-adherence. Khorana risk scores were calculated for each patient at outpatient clinics. In cases where the score was found to be >= 3, the consultant physician was informed. Results A total of 100 inpatients and 200 ambulatory patients were included in the study. The guideline adherence rates ranged between 59 and 100% for 5 out of 8 pre-defined criteria, whereas the rate for others remained at 0-1%. A significant increase was observed in the adherence rates for initiation of prophylaxis at admission and determination of correct dose of an anticoagulant after recommendations being implemented (p < 0.001, McNemar test). Eleven patients were identified as at high-risk of VTE at ambulatory setting; however, an initiation of an anticoagulant was not considered by the consultant physicians. Conclusion There are potential problems in implementation of guideline recommendations, which leads to low adherence rate. Therefore, liason with pharmacists and consultants for individual risk assessment and monitoring of patients will help to increase guideline adherence rates.