This paper investigates the relationships between the field of study mismatch, or horizontal educational mismatch, and the characteristics of employed individuals, as well as their satisfaction with various aspects of their career. Horizontal mismatch is defined as holding a degree in a field of study different from that required for one’s current job. Although understanding this phenomenon is important for shaping public policies, it has received considerably less attention than overeducation. The study draws on data from a local survey of 518 employed individuals in Poland and employs a series of logit models. The findings confirm the significant role of education-related variables and identify fields of study associated with higher and lower risks of mismatch. In contrast, variables such as gender, parenthood, and self-employment show no significant relationship with horizontal mismatch. The results further indicate that horizontal mismatch negatively affects satisfaction with education, employment, wages, career prospects, and job security. Mismatch also appears to be a gradable concept: individuals who are only partially matched report much higher satisfaction than those who are fully mismatched. The study additionally explores the relationship between horizontal and vertical mismatches and highlights the importance of distinguishing between these two forms of mismatch. The findings are discussed in the broader context of the voluntariness and persistence of mismatch.