Recently, a new preferential looking (PL) test has been presented for measuring visual acuity in infants and young children (Cardiff Acuity Test, CAT). The PL target is a schematic vanishing picture composed of isoluminant lines with different spatial orientations. Fifty-three healthy children (4-34 months, group 1), 28 (4-35 months) children at risk for amblyopia due to strabismus (group 2), 19 healthy subjects, and 157 patients (group 3) were tested with the CAT. In group 2 the CAT was compared with the fixation preference test. In group 3 the CAT was compared with a recognition test (Landolt C test). In group 1 the interocular difference of the CAT data was a maximum of 1 dB (70% 0 dB, 30% 1 dB, 1/3 so-called octave). Thus, an interocular difference of > 1 dB was considered to be suggestive of monocular or asymmetrical visual impairment. The maximum value 6/6 was frequently achieved (RE 44%, LE 36%, > 18 months RE 57%, LE 46%). In group 2 only 20% of the monolateral strabismic children showed an interocular difference > 1 dB in the CAT. In group 3 we found significant correlations between the CAT and Landolt acuity. A ratio of about 1.7/1 between CAT and Landolt acuity remained constant in cataract eyes as compared to healthy eyes. In amblyopic eyes due to strabismus this ratio was 3.7/1. Thus, amblyopia was underestimated with the CAT. Without limiting the examination distance, interocular differences > 1 dB in the CAT occurred in 52% of the strabismic amblyopic patients (potential sensitivity). At a distance of 1 m this rate decreased to 22% (real sensitivity). In conclusion, the CAT definitely lacks sensitivity for strabismic amblyopia. The data suggest that the real sensitivity could be improved by using higher spatial frequencies. The use of familiar shapes instead of gratings such as PL targets affects cooperation favorably in 12- to 36-month-old children.