A case-control study, on defau lting From DOTS was performed in three districts of ArsirnZone, Oramia Regional State, among patients registered during the period of July I, 1997rnto December 31 , 1999 to determine the rate of defaulting and to identify factors associatedrnwith it.rnA health record review of 1367 new tuberculosis patients put on DOTS during a period ofrn30 months (July 1997 to December 1999) was carried out in order to determine the rate ofrndefaulting. All the study subjects were registered and put on DOTS after June 30, 1997 andrncompleted treatment or declared cured before January 1,2000. The cases and contro ls wererntraced actively and interviewed by trained interviewers using a pre-tested structuredrnquestionnaire. The two groups were compared by social, demographic and health servicesrnvariables. The overall defaulter rate and specific rate by month of defaulting, healthrninstitutions, distri cts and distance from health institutions were calculated. All defaultersrnand the non-defaulters were selected by paired matching of sex and age using the lotteryrnmethod. Two controls were matched individually to each case.rnOne hundred fifty five cases and one hW1dred sixty controls were included in the study.rnThe overall defaulting rate froID DOTS was calculated to be 11.3%. The rate of defaultingrnin case of sputum smear positive pulmonatÂ·y tuberculosis was found to be 11 .6%. The raternof defau lting was higher in Etheya clinic and Hitosa District. Highest (80%) rate ofrnVIIrndefaulting occurred during the continuation phase. Medication side effect was found to bernsignificantly associated with defaulting from DOTS (OR= 4.20 with 95% CI 1.51 to 11.66).rnAdequate knowledge and family SUppOlt were found to be important poss ible protectivernfactors for defaulting (OR=0.04 with 95% CI 0.02 to 0.10 and OR=0.19 with 95% CI 0.08rnto 0.46 respectively). Distance from hea lth units and drug intolerance were the majorrnreasons mentioned for defaulting. However, there is no significant difference betweenrncases and controls regarding distance, employment status, attitude to treatment center, levelrnof education and average monthly income.rnThe rate is slightly higher than tlle critical level of 10% set by WHO. The major factorsrncontributing to high rate of defaulting were lack of family SUppOlt, inadequate knowledgernabout duration of treatment and presence of medication side effects. Health programmernthat are intended to enhance family support and knnwledge about duration of DOTSrntreatment and Drug tolerance should be strengthened.rnVlll