This study aimed to identify the factors affecting suitability of the cancer patients for drug clinical trials in Turkey. METHODS: A total of 1316 patients that admitted to 5 centers including university, and research and education (R&E) hospitals were included. RESULTS: Mean age of the patients was 57.2±14.0 years, and 50.3% (n= 662) were male. Mean age of the males were higher than the females (59.3±13.5 vs 54.1±14.1; p< 0.001). Most frequent cancer types were breast (22.6%), lung (15.3%), and colorectal cancers (10.7%). Most frequent treatment plans were for metastatic disease (61.2%), and first-line therapies (58.8%) in these metastatic patients. 54.4% (n= 716) of the patients were found to be suitable for recruitment to clinical trials. Mean age of suitable patients was lower than others (55.0±13.1 vs 59.6±14.5; p< 0.001). The proportions of suitable patients in university and R&E hospitals were 58% and 51.3%, respectively (p= 0.015). Females had higher suitability (%57 vs %52; p= 0.057). When disease types were assessed, breast (66%) and colorectal (65%) cancers, and lymphomas (63%) had highest, and sarcomas (39%) had lowest suitability (p< 0.001). suitability was 69% in adjuvant-planned, 52% in neoadjuvant-planned, 46% in metastatic, and 77% in chemoradiotherapy-planned patients (p< 0.001). Suitability decreased with increased metastatic treatment line (48% for first-line, 42% for second-line, and 36% for third-line). Most frequent barrier against suitability was living in a far city (45%). Other factors were absence of a histological diagnosis (1.7%), age (6%), poor performance status (34.5%), inadequate liver (6.5%), renal (8.8%), bone-marrow (2.2%), and cardiac functions (4%), cranial metastasis (7.3%), cord-pressure (2.2%), secondary cancer (3.7%), and participation to prior clinical trial (2.5%). CONCLUSIONS: Most significant factor for non-suitability for clinical trials in Turkey was living in a far city from the study center. Also, poor performance status, and insufficient organ functions also negatively affect suitability for clinical trials.