Down syndrome (DS) or trisomy 21 is the most common type of trisomy among children. Almost half of these patients are at risk for congenital heart disease, and a minority of them may suffer from leukemia. The association of congenital heart disease and leukemia may be life threatening. It is important to determine the factors that increase leukemia in CHD. In this descriptive crosssectional research, all patients with Down syndrome who referred to Neonatal, Pediatrics, Pediatric Cardiology, and Hematology Departments of Besat Hospital of Hamedan from 2010 to 2017 were included. Patients' data were obtained from paper and electronic records or phone calls (if needed), and then the data was analyzed. We used odd ratio and confidence interval to study the risk increase of leukemia. Total number of patients diagnosed with Down syndrome was 118 cases. 98 (83%) cases had congenital heart disease, among them 33 cases (33.6%) had history of angiography. The most common cardiovascular diseases were AVSD (30.6%), TOF (16.3%), ASD 2 (16.3%), and VSD (15.3%), PDA (14.2%). The most common type of leukemia was ALL. Among CHD (congenital heart disease) patients, 92 (78%) cases suffered only from congenital heart disease, and 6 (5.08%) of them had leukemia and congenital heart disease simultaneously, among them 4 (66%) patients had history of angiography (P = 0.078). Two cases had leukemia without CHD. The odds ratio of leukemia in patients with DS, in association of congenital heart disease was 1.70, and in patients who had history of angiography it was 3.93 with 95% confidence interval (0.686-22.63) (P > 0.05). Although angiography didn't statistically increase risk of leukemia in DS (P = 0.078), this risk increase can be clinically important.