Laparoscopy is regarded as the final decisive diagnostic test in suspected ectopic pregnancy. The new non-invasive diagnostic methods of transvaginal sonography and serum human chorionic gonadotrophin (HCG) monitoring now challenge this pivotal role of laparoscopy. In this prospective study the diagnostic value of an algorithm, combining transvaginal sonography with an HCG cut-off level between 1000 and 1500 IU/l (IRP) was tested in 208 consecutive women at risk for ectopic pregnancy. Three diagnostic categories are designated by the algorithm: intra-uterine pregnancy (n = 73), ectopic pregnancy (n = 89), and trophoblast in regression (n = 46). The latter category represents patients in whom no pregnancy could be located by transvaginal sonography, with an initial HCG concentration < 1500 IU/l, declining during follow-up. The algorithm has a sensitivity of 0.97, a specificity of 0.95, a likelihood ratio for a positive test of 19.4, and a likelihood ratio for a negative test of 0.03. The described diagnostic strategy thus proved extremely reliable in the safe management of patients at risk for ectopic pregnancy, and renders laparoscopy obsolete.