This report evaluates the validity of a preventive programme in a population which underwent refractometric screening at the ages of 20 months and 4 years. In 1987, 1,046 children born in 1985 in the territory of the Veneto National Health Unit No. 19 were invited to undergo screening for amblyogenic factors such as meridional hyperopia greater than or equal to +2.50 diopters (D), myopia less than or equal to -2.50 D, anisometropia greater than or equal to 2 D, opacity of the dioptric media and strabismus. The test method was non-cycloplegic photorefractometry (PhR). Seven hundred and ninety-five children were tested (76%); positive cases underwent subsequent cycloplegic autorefractometry (AR) and corrective lenses were prescribed as necessary. In 1989, an eye test was performed on 653 children who had taken part in the previous PhR screening and on 350 similar children who had not: the test included evaluation of visual acuity, stereopsis and AR. An eye with a corrected visual acuity of less than 0.7 was considered amblyopic. PhR demonstrated a sensitivity of 80%, a specificity of 96% and a positive prediction rating of 46% in the identification of amblyogenic factors. The prevalence of amblyopia at 4 years of age in the group which had undergone previous screening was 1.07% vs. 2.57% in the group which had not (P: not significant). The progress of the myopia was studied in a group with full optical correction used continuously (Group A) and in a control group under-corrected by at least 1.5 D (Group B).(ABSTRACT TRUNCATED AT 250 WORDS)