Background: Attention deficit/hyperactivity disorder is a common childhood-onset neurodevelopmental disorder that affects the child's psychosocial, educational, neuropsychological functioning self-esteem and quality of life from childhood to adulthood. It is estimated to affect about 5% of children and a third leading cause of disabilities. Objective: To assess the prevalence of attention deficit/hyperactivity disorder and its associated factors among children attending pediatric OPD in hospitals found in West Shoa zone, Central Ethiopia, 2020. Methods: Institution-based cross-sectional study was conducted from January 2020 to February 2020 among 422 children attending pediatric OPD in selected hospitals in West Shewa Zone and disruptive behavioral rating scale was used to collect data. OPD (out patient department) is section of hospital where patients who receive treatment without staying overnight are seen. Data were entered into Epi info version 7.1.2 and exported to SPSS version 21 for analysis. Descriptive statistics were done. Bivariate logistic regression was done to examine the relationship between different independent variables with attention deficit/hyperactivity disorder. Variable with p-value <0.05 was taken as statistically significant. Results: The prevalence rate of attention deficit/hyperactivity disorder (ADHD) among children attending pediatric OPD was 8.4%, 95% CI (5.9, 11.1). Being male (AOR= 3.35, 95% CI (1.52, 7.38), 9.39)), having a family size greater than five (AOR=3.95, CI (1.44, 10.11)), low family income (AOR=3.47, 95% CI (1.25, 10.10), presence of one or more psychosocial stressors (AOR=4.50, 95% CI (1.77, 9.42)), family history of mental illness (AOR= 3.6, 95% CI (1.78, 8.21)) and mothers having complication during pregnancy (AOR= 3.05, CI (1.10, 8.48)) were factors found to be associated with ADHD. Conclusion: Prevalence of attention deficit/hyperactivity disorder in this study is higher than global prevalence. This study has shown us ADHD is a public health issue that requires great emphasis and it is found to be associated with being male, younger age, large family size, low family income, psychosocial stressors, family history of mental illness and complication of pregnancy are factors associated with ADHD.