Australian Twin Registry The Australian Twin Registry is supported by a project grant from the National Health and Medical Research Council

Mid-Atlantic Twin Registry The Mid-Atlantic Twin Registry (MATR, pronounced "matter") is a population-based registry of 37,000+ twins of all ages who were born in or live in North Carolina , South Carolina , and Virginia.

The Danish Twin Registry The Danish Twin Registry (DTR) is one of the oldest twin registries in the world. It was established in the 1950'es with the aim of studying causes of cancer, and through the years it has gradually been expanded so that it now comprises twins born through more than 125 years.

National Twin Register of Sri Lanka NTR is an independent academic and research institution founded with the aim of establishing a register for twins in Sri Lanka , to facilitate study of twins. We aim to establish a centre of excellence for twin, sibling, family studies and genetic studies for the South Asian Region.

Massachusetts Twin Registry The Massachusetts Twin Registry is a group of adult twins who are permanent residents of Massachusetts . Enrollment in the Registry is voluntary. In the future, we will invite members of the Registry to participate in behavioral and biomedical research projects. Twins offer a unique opportunity to examine the influences of genetic and environmental factors on complex human characteristics .

The Minnesota Twin Family Registry A birth-record based Registry is nearing completion of some 8,000 pairs of twins born in Minnesota from 1936 to 1955, plus some 1,200 pairs of male twins born 1971-81.

CASTANET-the Cardiff Study of All Wales and NorthWest England Twins Registry The Cardiff Twin Registry was initially established by Professor A Thapar in 1992 and was expanded into the South Wales Twin Registry by Dr J Scourfield in 1997. The Greater Manchester twin registry was established by Professor A Thapar while working at the Royal Manchester Children's Hospital in 1996. The two registries were combined in 2000 and is currently based in the Department of Psychological Medicine at the University of Wales College of Medicine. The register contains approximately 6,0000 twin pairs..

Swedish Twin Registry The Swedish Twin Registry is the largest twin register in the world and includes more than 140,000 twins. The registry covers three different age cohorts, the older cohort, the middle cohort, and the younger cohort. The purpose of twin studies is to study the relative importance of genetic and environmental influences for behavioral characteristics and diseases.

The Finnish Twin Cohort Study The twin panel consists of two nationwide samples of the Finnish twin pairs. The first consists of like-sexed twin pairs born before 1958 and alive in 1975. The other sample of twin pairs born between 1958 and 1986 was compiled in 1987. The aim of the project is to study the environmental and genetic factors in selected common chronic diseases; especially cardiovascular diseases, common malignant tumors, and chronic obstructive lung diseases. Other diseases and risk factors for disease can also be studied.

Italian Twin Register