Purpose. The ethnically diverse Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study cohort provides a unique opportunity to explore associations among intraocular pressure (IOP), ethnicity, and refractive error while adjusting for potential confounding variables. Methods. Mixed linear models were used to examine the effect of age, refractive error (cycloplegic auto-refraction), ethnicity, sex, and measurement protocol on IOP (Tono-pen) in 3777 children, aged 6 to 14 years at their first CLEERE visit (1995-2009). Children who became myopic during follow-up were used to examine the relationship between time since myopia onset and IOP. Clinically meaningful differences in IOP were preset at >2 mm Hg. Results. IOP differed among refractive error categories with higher IOP in children with low/moderate myopia than those with high hyperopia (differences <1 mm Hg). There was a statistically significant relationship between age and IOP that depended on ethnicity (interaction p < 0.0001) and measurement protocol (interaction p < 0.0001). The relationship between sex and IOP depended on measurement protocol (interaction p = 0.0004). For children who became myopic during follow-up, the adjusted mean IOP showed a significant decline for only Asian (p = 0.024) and white children (p = 0.004). As with other statistically significant results, these changes in mean adjusted IOPs from 2 years before to 2 years after myopia onset were <2 mm Hg. Conclusions. Small but significant differences in IOP by refractive error category were found in this ethnically diverse cohort of children. Relationships between IOP and age, ethnicity, sex, and measurement protocol were complicated by significant interactions between these parameters. Longitudinal analysis of children before and after myopia onset showed changes in IOP over time that varied by ethnicity. Higher IOPs before and at myopia onset were not present in all ethnic groups, with differences before and after onset too small to suggest a role for IOP in the onset of myopia. © 2011 American Academy of Optometry.