In a national survey in China, 27,928 cases of leprosy detected by the health authorities between 1984 and 1998 were investigated. The delay between onset of symptoms (estimated from each case's recall) and confirmed diagnosis was < or = 2 years for 55.1% of the new patients but > 10 years for 7.0%, with a median value, overall, of 22.0 months. The median delay was longer: (1) for the multibacillary cases than the paucibacillary; (2) among farmers than among factory workers; (3) among some nationalities than among others (being longest among the Tu and shortest among the Wei); and (4) for some methods of case-detection than for others. Over the study period, the mean delay decreased with time. The delay was greatest in the areas where leprosy was endemic and/or where access to health services was poor. The later the cases were detected the more likely they were to show disability. Leprosy cases are still going undetected in China, although, over the last 14 years, case-finding has significantly improved. Age, occupation, nationality, leprosy type and detection method all appear to affect the delay.