This study focuses on the association of sibling sex-composition on socioeconomic outcomes in adulthood, where previous studies have found mixed results. Using Swedish administrative registers covering all biological siblings born between years 1960 and 1970 in two- and three-child families, the sex-composition of siblings is disentangled from their birth order and gender. The reported income magnitudes (measured as rank and absolute term) are small. In all, having a same-sex or opposite-sex sibling seems not to be an important family structural component for understanding socioeconomic outcomes such as income differences.