Dengue outbreak in Rohtas district in 2013 was investigated to determine the causes of current outbreak and to recommend remedial measures to overcome the current outbreak and prevent occurrence of outbreaks in future. Daily reporting of cases was ensured from the district in prescribed format. Epidemiological, entomological and environmental investigations in the affected areas were done to find out the factors contributing to the occurrence of the outbreak. Approximately, 1160 cases of dengue fever were reported from Rohtas district from 26 July till 14 Nov 2013. Age group affected most was 11–20 (32%)>21–30 (26%)>31–40 (19%). Males (66%) were more affected than females (34%). 11 out of 19 blocks were affected. Two Blocks viz:  Kochas (1101 case) and Dinara (22 case) were more affected. Approximately, 64 and 9 villages each in Block Kochas and Dinara were affected respectively. In Block Kochas incidence of the disease was more in village Kochas (510 case)> Parasthua (41 case)  > Gaura (18 case) while in Block Dinara incidence of the disease was more in village Geuda (3 case)>Harihardihara (3 case)>Dehri–on–Sone (2 case).73% of clinical samples were NS1 Ag positive while 27% were IgM ELISA positive. Entomological findings confirmed the presence of Aedine vector  in the affected  areas. Tyres were identified as the major aedine larval breeding site. Water storage in containers for long time was common in the affected areas. Finding confirms the factors leading to the present outbreak and highlights risk factors and control strategies to prevent future outbreak in the region. Community support and participation is also crucial for the prevention of future outbreaks and improving the health and well being of population in the districts.