The Government of the United Republic of Tanzania makes a lot of efforts to maintain peace and security in Kasulu District taking into account the presence of refugees in the district, but the area still faces a big challenge of insecurity. Therefore, the study was carried out in the villages which surround the refugee camps of Mtabila and Nyarugusu in Kasulu District to assess perceptions on the contribution of refugees to insecurity. The specific objectives were to: (a) find the laws and regulations that are most violated by refugees and local communities, (b) determine the extent to which refugees were involved in insecurity acts in the area, (c) assess positive and negative influence of the presence of refugees on security matters in the area, and (d) find ways by which insecurity affects the wellbeing of the people in the research area. Data were collected in October and November 2009 and analysed by using the Statistical Package for Social Sciences (SPSS) software. The results show that the laws that were most violated by refugees were leaving designated areas without permission, theft, being employed, and environmental damage. About the extent to which refugees were involved in insecurity acts, t-test results showed that the number points scored by non-Tanzanians and Tanzanians on an attitudinal scale that was used to gauge the extent were significantly different at the 0.1% level of significance (p = 0.000), which means that insecurity acts committed by refugees were contributing more to impoverishing natives than those committed by natives. It was also found that although the presence of refugees had many adverse effects including the insecurity acts they did, as seen above, and increase in prices of food and other commodities, it had some positive effects, which included provision of free health services to citizens in the refugee health centres and cheap labour from refugees who did casual labour employments. It was also found that insecurity acts committed by refugees were affecting the well-being of natives in various ways including loss of property through robbery by refugees, reduced time of working for fear of being attacked by refugees, and shortage of food due to some of it being stolen on farm by refugees. From the findings of the study it is concluded that insecurity has caused and continues to cause widespread social and economic impacts in Kasulu District. It also constrains development efforts of the people in the area. Based on the conclusion, it is recommended that refresher courses on security matters are required for security guards and leaders. Moreover, international organizations such as UNHCR and others should continue to provide services especially to the remaining refugees in the camps so as to improve their life and reduce their insecurity acts.