The relative age effect has been demonstrated in many youth and professional sports. Often, physical maturity compared to peers is emphasized as a causal mechanism (or at the very least a contributing factor) for these effects. The purpose of our investigation was to examine the relative age effect in a complex cognitive task with no significant physical requirements, more specifically among youth chess players. Data were analyzed 1) for all the registered Belgian youth chess players over the last 5 years (2009-2013) and 2) for the participants of the Belgian youth championship 2013. Results indicated an overall relative age effect among all Belgian youth chess players in the sample with the likelihood of participation significantly greater for players born in the first birth-date quartile (χ²=10.21, p<0.05; r= -0.77, p<0.01). Similarly, the likelihood of participation decreased when youth chess players were born in the last quartile of the year. These relative age effects were most prominent in the under 10 and under 8 year olds. There also appeared to be a performance-related relative age effect: statistically significant Kolmogorov-Smirnov tests (p<0.05) showed that players born in the first months of the selection year were more often in the top 10 of the Belgian Youth Championship 2013. Results suggest that cognitive maturity may be an important component of some RAEs, particularly in more technical, cognitively challenging sports. In addition, these findings may have implications for relative age related differences in skill acquisition among youth.