Abstract: Objective. The relationship between anxiety induction and changes in activity of the sympathetic nervous system (SNS) and parasympathetic nervous system (PSNS), as indexed by heart rate, heart rate variability, and skin conductance, and behavior performance were evaluated in children meeting criteria for multiple complex developmental disorder/borderline disorder (MCDD/BD). Method. Twelve children with MCDD/BD (mean age = 10.7, males to female ratio = 2:1) were compared to 14 children serving as normal controls (mean age = 10.5, and male to female ratio = 1.6:1). Physiological data (i.e., heart rate, high frequency (HF) and low frequency: high frequency ratio (LF:HF) of heart rate variability, breathing rate, and skin conductance) was continuously measured, while word recall performance was evaluated on four occasions across the four conditions: baseline (BL), condition one (C1), condition two (C2; stress condition), and condition three (C3; recovery condition). Serial sevens task was employed during the stress condition. Results. Analysis of variance with repeated measures showed significantly greater PSNS withdrawal, indexed by decrease in HF in normalized units, for children with MCDD/BD as compared to normal controls (F(1,24) 7.94, p=.01) and baseline, during stress ( t(1,11)=2.46, p=.031) and recovery conditions (t(1,11)=3.45, p=.005). Word recall performance was significantly lower in the MCDD/BD group (F(1,23)=12.56, p=.002) as compared to controls and appeared independent of physiology. Conclusion. This study found evidence of increased sensitivity to stress in children with MCDD/BD. The results indicate that children with MCDD/BD may have difficulty regulating anxiety as a result of a deficit in PSNS functioning.