Context: There are no available questionnaires in Spanish that assess the function and performance of shoulder and elbow in overhead sports. The Kerlan-Jobe Orthopaedic Clinic (KJOC) score is a reference tool for this purpose. We aimed to cross-culturally adapt and investigate its measurement properties in Spanish overhead athletes. Design: Cross-cultural adaptation followed the steps of direct translation, back translation, comprehensibility analysis, and review by the Committee of Experts. Then, symptomatic and asymptomatic overhead athletes were invited to complete an electronic version of the Spanish adaptation (KJOC-Sp). The structural validity was evaluated through an exploratory factor analysis with principal axis factoring. Hypotheses were tested for known-groups and convergent validity, studying the correlation with the Shoulder Pain and Disability Index and the Disabilities of the Arm, Shoulder, and Hand Sports Module questionnaires in symptomatic athletes. Cronbach alpha was calculated for internal consistency and intraclass correlation coefficient (ICC)_2,1 for test–retest reliability. Floor and ceiling effects and time to completion were also calculated. Results: The KJOC-Sp maintained the content of the original version and was adapted to the new population. One hundred participants (41 females and 59 males) with a mean age of 22.4 (5.9) years participated in the study of measurement properties. The factor analysis revealed a 1-factor solution. Symptomatic participants scored significantly lower than asymptomatic, with a large effect size (P < .001; r = .67). Correlations were of −.60 (P < .05) with the Shoulder and Pain Disability Index questionnaire and −0.66 (P < .05) with the Disabilities of the Arm, Shoulder, and Hand Sports Module questionnaire. Cronbach alpha was .98 (95% confidence interval, .97–.98) and the ICC_2,1 was .96 (95% confidence interval .93–.98). No floor or ceiling effects were observed among the symptomatic athletes, while mean time to completion was 121 seconds. Conclusion: The KJOC-Sp is equivalent to the original score, aside from valid and reliable, without floor or ceiling effects in symptomatic athletes and with a low time consumption.