Background <p>Adhesive capsulitis is a disabling musculoskeletal condition in individuals with diabetes mellitus, characterized by shoulder pain, limited range of motion (ROM), and functional impairment. Although exercise therapy is commonly recommended, evidence on resistance-band shoulder exercises in diabetic populations remains limited. This pilot randomized controlled trial evaluated the effects of a resistance-band shoulder exercise program in adults with diabetes and adhesive capsulitis.</p> Methods <p>In this stratified randomized controlled trial, 28 adults with diabetes and clinically confirmed adhesive capsulitis were assigned to a control group (<i>n</i> = 8), a type 1 diabetes exercise group (ExT1D, <i>n</i> = 9), or a type 2 diabetes exercise group (ExT2D, <i>n</i> = 11). The intervention consisted of supervised resistance-band stretching and strengthening exercises performed three times weekly for 8 weeks. Primary outcomes included shoulder ROM (flexion, abduction, internal and external rotation). Secondary outcomes were pain intensity (Visual Analog Scale) and functional disability (DASH and SPADI). Data were analyzed using ANCOVA with baseline adjustment.</p> Results <p>After baseline adjustment, significant between-group differences were observed in post-intervention shoulder ROM across all movements in both shoulders (<i>p</i> = 0.001), with large effect sizes. Both exercise groups showed greater improvements in ROM, pain reduction, and functional outcomes than the control group (<i>p</i> = 0.001), with no differences between ExT1D and ExT2D groups (<i>p</i> &gt; 0.05).</p> Conclusions <p>An 8-week resistance-band shoulder exercise program may improve shoulder mobility and reduce pain and disability in adults with diabetes and adhesive capsulitis. Larger randomized trials with longer follow-up are needed to confirm these findings.</p> Trial registration <p>Iranian Registry of Clinical Trials (IRCT), IRCT20180521039762N4, 02/02/2026. Retrospectively registered.</p>