The fourth survey of the Tromsø Study (Tromsø4), which was carried out in 1994-95, is the largest of the Tromsø Studies. This study included a total of 27,158 people (12,865 men and 14,293 women in the 25-97 age group). Everyone in Tromsø aged 25 or elder (born before 1970) was invited to participate in this study.
| Age | Men invited | Women invited | Male participants | Women participants | % men | % Women |
| 25-29 | 2919 | 3138 | 1515 | 1794 | 51,9 | 57,2 |
| 30-34 | 2651 | 2681 | 1556 | 1798 | 58,7 | 67,1 |
| 35-39 | 2474 | 2359 | 1649 | 1811 | 66,7 | 76,8 |
| 40-44 | 2324 | 2138 | 1681 | 1718 | 72,3 | 80,4 |
| 45-49 | 2094 | 1981 | 1604 | 1665 | 76,6 | 84,0 |
| 50-54 | 1595 | 1449 | 1306 | 1281 | 81,9 | 88,4 |
| 55-59 | 1077 | 1025 | 918 | 941 | 85,2 | 91,8 |
| 60-64 | 906 | 855 | 796 | 774 | 87,9 | 90,5 |
| 65-69 | 810 | 970 | 691 | 860 | 85,3 | 88,7 |
| 70-74 | 733 | 824 | 592 | 701 | 80,8 | 85,1 |
| 75-79 | 483 | 724 | 343 | 539 | 71,0 | 74,4 |
| 80-84 | 249 | 521 | 154 | 293 | 61,8 | 56,2 |
| 85-89 | 110 | 291 | 43 | 106 | 39,1 | 36,4 |
| 90+ | 55 | 122 | 17 | 12 | 30,9 | 9,8 |
| TOTAL | 18480 | 19078 | 12865 | 14293 | 69,6 | 74,9 |
If you do not take into account people who had moved or died before the study, the participation rate was 77 percent.
A brief questionnaire accompanied the invitation. The questionnaire included questions on general health condition, diagnosed heart and cardiovascular diseases or diabetes and history of heart and family cardiovascular diseases, muscle pains and physical discomfort, passive smoking and smoking habits, physical leisure activity, coffee, alcohol and fat consumption, education level and current work situation. Measurements of height, weight and blood pressure were taken. A blood sample was also taken to measure serum total cholesterol, HDL cholesterol, triglycerides, gamma-glutamyltransferase (GT), haemoglobin and blood cell count ("plot"). People who attended the study received another questionnaire that they were asked to complete and send back. Separate questionnaires were prepared for people aged under 70 and for those aged 70 or elder.
Everyone in the 55-74 age group, along with 5-10 percent in the 25-54 and 75-85 age groups were given the opportunity to undergo an extensive special study. A total of 7965 people accepted this offer. This included also measurement of bone density as a part of the TROST study
Tromsø4 provided the opportunity for a host of longitudinal studies, in which findings from previous studies could be compared with findings that were currently being collected. Examples included showing how age influences the development of obesity (Jacobsen et al, 2001) over a 20-year period, and if people who in 1979 had high cholesterol still suffered from this 15 years later (Wilsgaard et al, 2001).