Microtropia is an unilateral strabismus of less than 5 degrees, usually with harmonious anomalous correspondence. Three forms may be distinguished: Primary constant, primary decompensating and consecutive microtropia. In three instances microtropia is important for the ophthalmologist: In assessment of amblyopia apparently without strabismus, in evaluation of strabismus treatment results and in evaluation of hereditary factors in strabismus. Amblyopia is more pronounced in cases with anisometropia and eccentric fixation, but usually responds well to occlusion treatment. Because of a typical 'reading amblyopia', treatment with alternating partial occlusion should be carried out until a child can read fluently with each eye. It is estimated that about 1% of general population has a microstrabismus. Primary microtropia is probably due to a primary sensorial defect, which predisposes to anomalous retinal correspondence. Primary microtropia may decompensate into a larger angle. After therapy, not a complete parallelism but a consecutive microtropia results.