OBJECTIVE: To measure the level of the intraocular straylight in a group of pseudophakic eyes with monofocal posterior chamber intraocular lens and clear capsule. STUDY DESIGN: The intraocular straylight, measured 1 week after lens implantation, was compared with the intraocular straylight of a cataract group and a control group. The cataract surgery was standardized with capsulorhexis, phacoemulsification of the nucleus and intracapsular implantation of monofocal lens. SETTING: Out-patient, St Erik's Eye Hospital. SUBJECTS: Ten patients with intraocular lens, 10 pre-operative cataract patients, 10 persons with clear lens. MAIN OUTCOME MEASURES: The intraocular straylight was measured with a psycho-physiologic, direct compensation method using a straylight meter. The straylight induced by a light source at three different angles was investigated. RESULTS: There was no statistically significant difference in the straylight level between the intraocular lens group and the control group. The straylight level in these two groups were significantly different from the cataract group. There was no significant difference in the level of straylight induced by the three angles. There was no linear relation between the vision and the intraocular straylight. CONCLUSIONS: The result showed that the intraocular straylight was greatly reduced after cataract operation with implantation of monofocal intraocular lens. The straylight in the pseudophakic eyes was similar to that of the eyes with clear lenses. Sampling at one angle would be enough to obtain the information on the intraocular straylight in the pseudophakic and cataract patients. The intraocular straylight can be used as a parameter to estimate the optical quality of the eye.