BACKGROUND Oral cancer is the most common malignant tumor among head and neck cancers. Delay in diagnosis affects the treatment and prognosis of oral cancer. We measured the professional delay in the diagnosis and its attributes in the Cancer Institute of Iran, the largest referral center for oral cancer patients in the country. METHODS We interviewed oral cancer patients to measure the delay and used case-control approach to study association of various prognostic factors with professional delay and tumor stage. RESULTS Out of 206 patients, 71.4% were diagnosed at the advanced stage. The median of the patient, professional and total delays were 45, 86 and 140 day, receptively. In the univariate model, prescription of medicines like analgesics (OR = 5.3, 95% CI 2.2-12.9) and history of dental procedure (OR=6.8, 95% CI 1.7-26.9) were associated with higher risk of delay compared to patient who were biopsied from the beginning. History of loose teeth increased risk of delay 4 times (OR = 4.0, 95% CI 1.6-9.8). Patients with primary education had 70% lower risk of delay compared to the illiterate patients (OR = 0.3, 95% CI 0.1-0.7) and the risk was lower among patients who had diploma (OR = 0.04, 95% CI 0-0.7) and college education (OR = 0.1, 95% CI 0-0.4). The delayed patients were diagnosed in more advanced stage compared to the patients without delay (OR = 2.1, 95% CI 1.0-4.4). CONCLUSIONS Development of a national guideline for follow-up of oral lesions, training and awareness of health care professionals about oral cancer diagnosis may decrease the delay and improve the oral cancer outcome in Iran.