||BACKGROUND: The aim of this study was to investigate socio-economic inequalities in health care utilization from the 1980s and through the last 3 decades in a Norwegian county population. METHODS: Altogether, 166 758 observations of 97 251 individuals during surveys in 1984-86 (83% eligible responses), 1995-97 (51% eligible responses) and 2006-08 (50% eligible responses) of the total population of adults (>/= 20 years) from Nord-Trondelag county in Norway were included. Health care utilization was measured as at least one visit to general practitioner (GP), hospital outpatient services and inpatient care in the past year. Socio-economy was measured by both education and income and rescaled to measure relative indexes of inequality (RII). Relative and absolute inequalities were estimated from multilevel logistic regression. Estimates were adjusted for age, sex, municipality size and self-reported health. Results: GP utilization was higher among individuals with higher education in 1984-86. Among men the RII was 0.54 (CI: 0.48-0.62), and among women RII was 0.67 (CI: 0.58-0.77). In 2006-08, the corresponding RII was 1.31 (CI: 1.13-1.52) for men and 1.00 (CI: 0.85-1.18) for women, indicating higher or equal GP utilization among those with lower education, respectively. The corresponding RIIs for outpatient consultations were 0.58 (CI: 0.49-0.68) for men and 0.40 (CI: 0.34-0.46) for women in 1984-86, and 0.53 (CI: 0.46-0.62) for men and 0.47 (CI: 0.41-0.53) for women in 2006-08. Conclusion: Through the last 3 decades, the previous socio-economic differences in GP utilization have diminished. Despite this, highly educated people were more prone to utilize hospital outpatient consultations throughout the period 1984-2008.