<p>Climbing is a physically demanding discipline that places repetitive mechanical load on the upper limbs, potentially leading to morphological adaptations or overuse injuries. Despite this, musculoskeletal ultrasound (USI) has been underutilized in climbing research. This study aims to investigate sex and limb dominance related differences in forearm muscle and nerve morphology in climbers and to determine whether these structural features can predict climbing specialization (bouldering vs. lead climbing). A cross-sectional study was conducted with 50 recreational climbers (33 males). Ultrasound imaging was used to assess the thickness of forearm muscles (brachioradialis, pronator teres, flexor digitorum superficialis/profundus, pronator quadratus) and the median and radial nerves cross sectional area. Significant sex differences were observed for all muscles and the median nerve (<i>p</i> &lt; 0.001), with males exhibiting greater thickness; after adjustment for body size and training, the differences in the brachioradialis, flexor digitorum superficialis, flexor digitorum profundus and pronator quadratus remained significant, whereas those in the pronator teres and median nerve did not. No differences were found for the radial nerve or between dominant and non-dominant limbs. Flexor digitorum profundus (FDP) thickness predicted lead climbing, with each 1-mm increase raising the odds of being a lead climber by approximately 57% (OR = 1.573); the model showed acceptable discrimination (AUC = 0.775), and the FDP association persisted after adjustment for climbing experience and training volume. Ultrasound-based assessments revealed sex-related morphological differences in climbers’ forearm musculature. Greater FDP thickness is strongly associated with lead climbing specialization. These findings suggest that USI may be a valuable tool for profiling climbers, guiding training programs, and informing injury prevention strategies.</p>