The Eugenic Protection Act in Japan was amended in respect of the viability limit of gestation from 24 weeks to 22 weeks in 1991, because of the rapid progress of survival rate of extremely low birth weight infants in recent years. At Tokyo Women's Medical College, 112 out of 134 (84%) infants whose birth weight were less than 1,000 grams survived in the past 6 years. The effect of this amendment on perinatal and neonatal health care is discussed from medical, ethical and socioeconomic aspects. Viability is defined as not only "the ability to live" but also "the ability to grow and develop normally." The fundamental thought underlying ethics on viability of extremely premature infants are "recognition of continuity and discontinuity" and "human principle and life principle."