The Massie-Campbell Attachment During Stress Scale (ADS, Massie & Campbell, 1983) is an observation guide of the interactions between mothers (or caretakers) and children from 6 to 18 months. This study sought the construct validity (convergent and discriminant) of ADS, as well as its criterion validity (sensitivity, specificity, and predictive values). To that end, child attachment was measured in a group of 32 children aged 8 to 10 months from Lima, Peru using ADS and Attachment Q-set 3.0 (AQS, Waters, 1995). Maternal sensitivity was assessed as well. It was found that ADS attachment classifications were related to AQS attachment security continuous scores r(= .41, p = .02) and to its dichotomous classifications [secure vs. insecure; Χ2 (1, N = 32) = 4.69, p = 0.03, d = 0.83]. Additionally, no significant differences between the ADS’s maternal sensitivity of mothers with children classified ass ecure and mothers with children classified as insecure were found. Since ADS’s sensitivity did not reach satisfactory levels (33.3 %, 95 % CI = [15.48, 56.90]), a cut-off point of 5 secure behaviors was used, which improved its sensitivity (47.6 %, 95 % CI = [26.4; 69.7]) while maintaining satisfactory levels of specificity (90.9 %, 95 % CI = [57.1; 99.5]). The instrument shows adequate convergent validity but lacks evidence of discriminant validity. Further exploration of ADS’s sensitivity, specificity, and predictive values is recommended in order to obtain a cut-off point with greater validity, given that the instrument is considered a screening test.