This study aimed to investigate the impact of shoulder dysfunction on concomitant neck disability in patients with shoulder disorders. The participants were patients with subacromial impingement syndrome (SIS) and frozen shoulder (FS). Twenty patients with SIS and 21 with FS without cervical radiculopathy were enrolled. The participants were assessed for the 4-week prevalence of neck pain, Neck Disability Index (NDI), shoulder strength and range of motion, a short version of the Disabilities of the Arm, Shoulder, and Hand questionnaire (quick-DASH), and the Pain Catastrophizing Scale (PCS). The 4-week prevalence of neck pain was 12 out of 20 (60%) in patients with SIS and 13 out of 21 (62%) in patients with FS. The median NDIs were 13 and 12 for SIS and FS, respectively, with no statistically significant difference. About 41% (17/41) of the participants displayed an NDI greater than the cutoff value for disability in daily living. Although shoulder abduction strength correlated with the NDI in patients with SIS, the PCS score correlated with the NDI in patients with FS. Concomitant neck disability is a critical concern for patients with shoulder disorders. The clinical factors related to concomitant neck disability differ between SIS and FS, with specific interventions recommended for each condition.