Of 656 patients with ALL (all types) diagnosed in Switzerland during 4 consecutive 4-year periods (1976-1979, 1980-1983, 1984-1987, 1988-1991), 507 were officially registered on protocols ("study" patients) while 149 were not ("nonstudy" patients). The mean incidence of 3.8/100,000 children < 15 years/year is higher than reported for other Western countries. Evidence is presented suggesting that the 656 patients represent only approximately 90% of all children with ALL residing in Switzerland, indicating that the true incidence of ALL might even be higher. The fraction of "nonstudy" patients fell from 40% (1976-1979) to 15% (1984-1987). The rate of survival at 4 years of all patients with ALL ("study" and "nonstudy") increased by 17% during the three consecutive periods 1976-1979, 1980-1983, and 1984-1987. As expected, a higher increase (20%) was observed in "study" patients and a statistically nonsignificant lower one (10%) in "nonstudy" patients.