Abstract: Background: The existence and control of Dengue Hemorrhagic Fever (DHF) are closely related to its vectors. Larval density and key breeding sites play important roles in determining the most suitable and effective methods for vector control. Materials and Methods: The present study identified the common breeding places for both Aedes aegypti and Aedes albopictus and examined larva density and the impact on dengue transmission. An entomological survey was carried out in Medan and Langkat in 304 households in both districts. Result: Aedes aegypti and A. albopictus were found in 11 and 12 out of 18 types of water containers, respectively, in both high and low incidence districts. Aedes aegypti larvae were found in most indoor bathtub containers. By contrast, A. albopictus larvae were found in most outdoor pail containers both in high and low incidence districts. Conclusion: The larval indices for A. aegypti, which is predominantly found in Medan and for A. albopictus larvae, which is predominantly found in Langkat were 33, 12 and 39 and 13, 5 and 18, respectively. The House Index (HI) was a determinant of DHF transmission in North Sumatera province. According to the WHO, the larval density figures of HI, Container Index (CI) and Breteau Index (BI) in Medan and Langkat were 5, 4 and 5 and 3, 1 and 2, respectively. Thus, the density figure of larval indices in Medan was higher than in Langkat (4.7 and 2, respectively). Based on the WHO standards, both districts have HI values higher than 10, which indicates that both high and low DHF incidence districts have a high risk for DHF transmission and the probability of transmission for DHF in Medan was higher than in Langkat.