In Singapore, cancer incidence is documented separately for the different Chinese dialect groups, as a means of providing a possible insight into environmental or genetic factors which may be involved in the aetiological process. Thus, it would be useful to determine whether or not the Chinese population in Singapore still comprises distinct dialect groups. In view of this, an investigation into the dialect group of the parents of 792 hospital in-patients (cases and controls) was carried out. It was found that the vast majority of patients (94.2%), most of whom were born before 1940, had parents of the same dialect group. The percentages of within-dialect marriages were only slightly less for offspring born in Singapore or Malaysia as opposed to China, and decreases with time were small. Thus in 1985-87 Chinese cancer patients and controls in Singapore, of the ages represented in this study may indeed be classified according to their father's dialect and this is likely to be the case for at least the next decade or so. This finding will be of use to cancer epidemiologists as well as others studying Chinese dialect group variations in disease patterns.