Background and objectives: The aim of the study is to identify factors related to comorbid oppositional defiant disorder (ODD) and anxiety disorders (ADs). Design: A sample of 622 children was assessed longitudinally at 3 and 5 years of age. Methods: At baseline, there were 310 boys (49.8%), most participants were of Caucasian-white ethnicity (89.1%) and attended to public school (64.0%), and families’ socioeconomic status was 64.3% medium-high, 14.1% medium and 20.5% medium-low. Children diagnosed with ODD and/or AD were selected: n = 103 at 3 years of age (44 ODD, 42 AD and 17 ODD + AD) and n = 106 at 5 years of age (31 ODD, 60 AD and 15 ODD + AD). Results: High levels of the child’s negative affectivity and the mother’s aggressive behavior (versus AD), and high scores in the father’s psychopathology measurements (versus ODD) were related to the presence of comorbid ODD + AD at 3 years of age. High scores in approach-positive anticipation, fears (only in boys, in girls the reverse effect occurred) compared to ODD and AD independently and aggressive behavior (versus AD), and low scores for smiling and laughter (versus ODD only and AD only) were predictive of comorbidity at the 5 years of age. Conclusions: Temperament traits may be a common factor in explaining longitudinal ODD + AD comorbidity.