Stereoacuity was investigated in 3- to 5-year-old children and in adults by using four commercially available stereotests (the Frisby, Randot circles, Random-Dot E (RDE), and TNO tests) and by using an experimental stereotest. Comparative reanalysis was also made of data obtained from other studies of the RDE and Titmus circles tests. Stereoacuity norms are proposed for 3- to 5-year-old children for each of the commercially available tests. Factors influencing stereoacuity threshold differences among the different tests are discussed. The results on all tests are consistent with the hypothesis that binocular visual development is incomplete at 5 years of age.