The aim of this study was to assess endometrial thickness using transvaginal sonography in a representative sample of postmenopausal women and to evaluate whether the technique can be used for screening of endometrial cancer. A random sample (n = 1000) of the total population of women aged 45-80 years resident in the city of Göteborg in 1993 was invited to attend for transvaginal sonography. The only exclusion criterion was hysterectomy. Transvaginal sonography was performed in 827 women. An endometrium of < or = 4 mm was not investigated further. Women with an endometrium of 5-7 mm and non-measurable cases were re-assessed 1 year later, and women with an endometrial thickness of > or = 8 mm were investigated directly with hysteroscopy and/or dilatation and curettage. A total of 559 women were postmenopausal and 183 were taking some form of hormonal substitution (33%). One case of endometrial cancer (endometrial thickness 19 mm), 23 cases of polyps without atypia (endometrial thickness 8-18 mm) and no cases of endometrial hyperplasia were diagnosed. Endometrial thicknesses were as follows (mean +/- SEM; respectively grouped as < or = 4 mm, 5-7 mm and > or = 8 mm): total population of postmenopausal women (3.4 +/- 0.1 mm, 82%, 13% and 6%); postmenopausal women without estrogens (3.0 +/- 0.1 mm, 90%, 7% and 3%); postmenopausal women on medium-potency estrogens + gestagen (5.1 +/- 0.3 mm, 49%, 40% and 11%) and women with low-potency estrogens only (3.6 +/- 0.3 mm, 85%, 6% and 9%). The prevalence of endometrial cancer was 0.2% and for benign polyps 3.2% in this representative sample of postmenopausal women. Our results do not support generalized endometrial screening with transvaginal sonography.