Background: Tuberculosis (TB) remains a major global health problem. Delay in tuberculosis diagnosis may worsen the disease and increase transmission within the general population. This study estimated the prevalence of diagnosis delay and its determinants. Objective: To measure the magnitude of patient and health service delay and identify the factors associated with the delay. Methodology: A facility based cross-sectional study design was conducted at the three hospitals of Arsi Zone from December 2014-March 2015. All above 15 years old, all forms of TB patient who were on intensive phase and who were diagnosed during the data collection period were included in the study. Data were collected using semi-structured questionnaire and patient record review. Binary and multivariate logistic regressions were done using SPSS Ver. 20, to investigate determinants of patient, health system and total dely. The P-value of <0.05 was taken as significance. Result: Three hundred sixty two (362) all forms of TB patients enrolled in the study, of which 36.7% experienced patient delay, 49.7% health system delay and 48.9% total delay. The median patient, health system and total delay were 30, 9, 40 days respectively. The Health Extension Workers (HEWs) should be supported to strengthen the activities of health education. A well-designed information education, communication/behavioral change communication (IEC/BCC) strategy for TB might improve the TB control program.