As part of an international collaborative study, an attempt was made to identify all cases of breast cancer among residents of the Cities of Athens and Piraeus newly diagnosed in a period of 2 1/2 years. A total of 956 cases was identified, giving an annual average incidence rate of 34.9 per 100,000 female population. Rates by age and marital status are reported.

Of these cases 799 (84%) were interviewed, along with 2,470 controls. The controls were residents of Athens and Piraeus under treatment in the same hospitals as the breast cancer cases but for conditions other than breast cancer. In relation to the controls, the breast cancer cases were of low fertility. After adjustment for this difference there was no difference between cases and controls in any of a variety of measures of lactation experience.

The cases differed significantly from the controls in having higher socio-economic status, earlier menarche, later first pregnancy, later menopause and greater height and weight. The ranges of these variables were associated with variations in breast cancer risk of the order of two or three fold.