Objective: To evaluate the reliability and validity of the English and Spanish versions of the Strengths and Weaknesses of ADHD-symptom and Normal-behavior (SWAN) rating scale. Method: Parents of preschoolers completed both a SWAN and the well-established Strengths and Difficulties Questionnaire (SDQ) on two separate occasions over a span of 3 months; instruments were in the primary language of the family (English or Spanish). Results: Psychometric properties for the English and Spanish versions of the SWAN were adequate, with high internal consistency and moderate test-retest reliability. Skewness and kurtosis statistics for the SWAN were within the range expected for a normally distributed population. The SWAN also demonstrated adequate convergent and discriminant validity in correlations with the various subscales of the SDQ. Conclusion: Psychometric properties of both the English and Spanish versions of the SWAN indicate that it is a reliable and valid instrument for measuring child attention and hyperactivity. The stability of ratings over time in this preschool sample was moderate, which may reflect the relative instability of these characteristics in preschool children. (Contains 2 tables.)