With the recent development of high-resolution real-time ultrasonic devices and their application to clinical examination and breast screening, small non-palpable breast lesions have frequently been detected and controversy has arisen concerning their diagnosis and treatment. In order to evaluate the relationship between ultrasonic B-mode images and palpability of breast tumors, 71 breast tumors including 21 cancers were analyzed. Five basic measurements on tumor size and location were performed followed by calculation of secondary parameters of palpability. Larger size (D and W), less distance from the skin surface (S-T), less embeddedness within or more protrusion from the mammary gland (G-T) and greater relative size of tumor with respect to whole breast thickness (D/(S-P)) were found to be significantly related to greater palpability of breast tumors. Among the qualitative diagnostic criteria for breast tumors, an irregular shape, rough border, thick boundary echoes, heterogeneous internal echoes and indirect signs were statistically more frequent in palpable than non-palpable tumors, and in malignant than in benign tumors. In cases of cancer, palpability was related significantly only to size and to heterogeneous internal echoes. For early detection of breast cancer, identification of breast cancer among small non-palpable breast lesions less than 1 cm in size in ultrasonic B-mode images is considered to be essential.