Most bird species display sexually dimorphic traits. In contrast to this general rule, both males and females of the Middle Spotted Woodpecker present a carotenoid red cap, which constitutes mutual ornamentation. In our study we investigated whether pair members are matched in terms of the brightness of this ornament. We also examined the similarity between mates in red cap size as well as biometric parameters, such as weight and the length of the wing, beak and tarsus. We found that males and females within pairs were positively assortatively mated with respect to the red cap brightness as well as body weight. We found no similarity between pair members neither in red cap size nor the length of wing, beak or tarsus. We discuss our findings in the light of mutual mate choice, social competitions and other factors that may account for the similarity in expression of the red cap in the studied species.