Disclosure of the diagnosis of cancer to patients is a difficult task for physicians in developing countries. Family members often oppose truth telling. The aim of this study was to evaluate the incidence of the "do not tell" attitude in a general population of cancer patients and to explore the factors affecting the attitude of cancer patients' relatives about honest disclosure. Using a questionnaire, relatives of 150 patients with recently diagnosed cancer were interviewed. Of the relatives, 66% did not want the diagnosis to be disclosed. Male gender of the patient, a diagnosis of a non-breast cancer malignancy, the presence of stage IV disease, no previous request for disclosure by the patient, insufficient knowledge of the relative about cancer in general, and stronger religious belief of the relative were associated with greater likelihood of the relative having a "do not tell" attitude in univariate analyses ( P=0.032, P=0.000, P=0.051, P=0.021, P=0.128, and P=0.058, respectively). In a multivariate analysis, the diagnosis of a non-breast cancer malignancy, and insufficient knowledge of the relative about cancer in general retained their significance (exp(B)=14.77, P=0.000; exp(B)=3.04, P=0.01, respectively). Differences among different countries and cultures are discussed.