Abstract Background Reliable and valid measurement of early child development are necessary for the design of effective interventions, programs, and policies to improve early child outcomes. One widely used measure in low- and middle-income countries (LMICs) is the Bayley Scales of Infant and Toddler Development III (Bayley-III). Alternatively, the Bangladeshi-adapted Ages and Stages Questionnaire Inventory (ASQ:I) can be administered more quickly, inexpensively, and with less training than the Bayley-III. We aimed to assess the concurrent validity of the Bangladeshi-adapted ASQ:I with the Bayley-III in children 4–27 months old in rural Bangladesh. Methods The sample was a sub-sample (n = 244) of endline participants from an evaluation of an early child development intervention (July–August 2018). We assessed concurrent validity between internally age-standardized domain-specific and total scores using Pearson correlations both overall and stratified by age and intervention status. We also assessed correlations between scores and variables theoretically related to child development including maternal education and stimulation in the home. Results The overall correlation between ASQ:I and Bayley-III total scores was moderate (r = 0.42 95% CI: 0.30–0.53), with no systematic differences by intervention status. Overall, concurrent validity was highest for the gross motor domain (r = 0.51, 0.40–0.60), and lowest for the fine motor domain (r = 0.20, 0.04–0.33). Total ASQ:I and Bayley-III scores were positively correlated with child stimulation and maternal education. Conclusion The Bangladeshi-adapted ASQ:I is a low-cost tool that can be feasibly administered in rural Bangladesh, is moderately correlated with the Bayley-III, and can be used to measure child development when human, time, or financial resources are constrained.