Purpose <p>This study examined the association between food selectivity—a common nutrition-related behavioral challenge—and constipation and overall gastrointestinal (GI) symptom severity in children with autism spectrum disorder (ASD).</p> Methods <p>In this cross-sectional study conducted in Türkiye, 105 parents of children aged 4–10&#xa0;years completed a questionnaire assessing demographic characteristics and eating habits. Food selectivity/mealtime behaviors were evaluated using the brief autism mealtime behaviors inventory (BAMBI). GI symptom burden was assessed with a GI symptom severity index, and functional constipation was evaluated using Rome III diagnostic criteria.</p> Results <p>Based on the GI severity index, 41.0% of children were reported to have constipation. The GI severity index showed a positive, weak but significant correlation with the BAMBI total score (r = 0.353, p &lt; 0.01). Consistently, the limited food variety subdomain of BAMBI was positively correlated with GI severity (r = 0.196, p &lt; 0.05). The constipation subscore was positively correlated with the overall GI severity index score (r = 0.291, p &lt; 0.01). Moreover, constipation was correlated with Rome III functional constipation (r = 0.226, p &lt; 0.05).</p> Conclusion <p>In children with ASD, greater food selectivity—particularly reduced dietary variety—was associated with higher GI symptom burden and constipation. These findings highlight the importance of assessing food selectivity and dietary diversity when addressing constipation and GI complaints in children with ASD.</p>