Tanzania integrated a historical large number of refugees in 2010 when 162,156 refugees were integrated at once. This article explores whether integrated refugees at Katumba Old Settlement in Tanzania are practising behaviours that threaten national security or not. This work was guided by Tom Kuhlman’s Comprehensive Model of Refugee Integration (1991) as its framework for analysis. Using a survey with a sample of 397 respondents and 31 key informant interviews, the study found that the integrated refugees pose threat to national security. A significant percentage of respondents indicated that integrated refugees: network with relatives and friends to come into Tanzania illegally; host illegal migrants; create social exclusionary networks and are unwilling to accept Tanzania’s core values and behaviours. Efforts to increase awareness among integrated refugees on their rights and responsibilities as new Tanzanian citizens as well as enforcement of laws are suggested as solutions for mitigating these behaviours.