Socioeconomic inequalities in health status and health behaviour are reflected in different patterns of healthcare use between socioeconomic groups. Individuals with a low social economic status (SES) incline to use more acute healthcare services, such as provided by out-of-hours primary care services (OPCSs), than high SES individuals. This in turn could reinforce socioeconomic health inequalities. Better understanding of the extent to which socioeconomic inequalities in OPCS use exist, enables a more targeted approach in facilitating appropriate care at the right time and place, and in fostering the sustainable use of resources. The studies reported in this dissertation consistently show associations between OPCS use and SES: reflected in higher use within each lower level of SES. These inequalities were found by comparing OPCS use between neighbourhoods and between individuals, using different measures of SES. Socioeconomic inequalities could not be explained by the patient’s health status or by the reforms of long-term care. Rather, it may be a more complex interplay and accumulation of health and social problems in low SES groups that increase their vulnerability for ‘medically inappropriate’ use of health services, which is reflected in higher OPCS use. The findings of our studies in the context of existing literature suggest that the healthcare system does not connect properly with the capacities of socioeconomically vulnerable individuals and OPCSs seemingly meet up to an unfulfilled need. Therefore, health and social care should be targeted better to socioeconomically vulnerable individuals in facilitating equal care for equal need in the appropriate healthcare setting.