Osteoporosis is a disease characterised by a low bone mineral density (BMD) and microarchitectural deterioration of bone tissue leading to fractures, especially of the hip and spine. It is a major public health problem of western societies that affects the elderly population. Both environmental and genetic factors have been evoked as determinants of peak bone mass, but the major determinant of BMD is heritability. Families were recruited as part of an ongoing study to identify susceptibility genes to low BMD. Osteoporotic and osteopenic women were identified retrospectively from records at the Bone Densitometry Unit of Cork University Hospital. Individuals with a disease or on medications known to influence calcium metabolism were excluded. Participants were requested to nominate both female and male relatives for bone densitometry measurement. Relatives over 40 years of age, with a history of fracture or dowager’s hump were preferentially selected for inclusion in the study. Of the 220 families who participated in the study to date, relative pairs with low BMD were found in 152 families. There was a total of 525 low BMD pairs among the 152 families, of whom 310 were sib-pairs. Our study will help to increase public awareness in Ireland of the familial risk of osteoporosis.