The purpose was to establish the inter-examiner variability and agreement between more than two examiners assessing children and adult patients. The study involved four experienced examiners. The alternate prism cover test (APCT) was conducted at near and distance in 41 subjects with horizontal strabismus (21 male and 20 female) with a median age of 12 years (3-74). Twenty-five were exo and 16 eso deviations. Twenty-two were manifest, 13 intermittent and six latent deviations. Inter-examiner variability between APCT measurements performed by two examiners ranged from 6.9 to 12.5PD dependent on the examiner pair and fixation distance. Slightly larger variances were found for near versus distance fixation. A value of 10PD is suggestive of real change at near and 9PD for distance. Angle of deviation, test distance and age had no significant influence on variations.