A consecutive series of 185 instances of histologically confirmed nonpalpable infiltrating carcinoma of the breast is presented. Histologic nodal involvement was found in 12 per cent and was dependent on the size of the tumor. Conservative surgical treatment was the predominant method used during the study period. The ten year over-all survival was studied and compared with that of 4,217 instances of palpable carcinoma of the breast observed during the same period. The ten year survival rates were, by far, better for nonpalpable (94 per cent) than for palpable carcinomas (65 per cent). A better prognosis for nonpalpable carcinomas was confirmed also by multivariate analysis (Cox) with adjustment for potential confounders, such as age, stage or nodal involvement. The possible confounding effect of over diagnosis and length or lead time bias is discussed. Although this difference in survival might be partially explained by the aforementioned confounders, the chance of increasing life expectancy and conservative surgical treatment encourages preclinical detection of carcinoma of the breast.