An oculometric study has been performed to evaluate features possibly being responsible for a (permanent) shift towards myopia in eyes of diabetics, a trend apparent from previous clinical investigations. Having excluded cases of transient refractive change associated with poor metabolic control, we are dealing with adult subjects with stable refractive levels, also including cases of adult-onset myopia. Out of 62 diabetic and 48 non-diabetic eyes (age 17-23, diabetes duration 2-38 years) a careful matching according to age, sex and refraction provided 26 eye-pairs from 52 subjects for analysis. In 23 matched pairs there was low myopia. The lenses of diabetics appeared significantly thicker than in non-diabetics (mean difference 0.2 mm), and a higher lens power came close to significance. Corneal curvature, anterior chamber depth and axial length did not differ. A subsequent analysis of degree of lens thickness increase in diabetics revealed a positive correlation with diabetes duration. A thicker lens does not of necessity imply a higher lens power, but from the present data this is the most likely explanation of diabetic myopia in adults.