Analysis of perinatal mortality in newborn infants with a birth weight of less than 1000 grams in Hospital San Cecilio in Granada (Spain) over the 1991-2010 period ABSTRACT Introduction. Perinatal mortality has significantly decreased over the last decades. Low birth weight and prematurity are amongst the strongest predictors of neonatal death. The main objective is to analyze the evolution of perinatal mortality and its causes in newborn infants with a birth weight of less than 1000 grams over the last 20 years (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010). Population and Methods. Observational, descriptive, longitudinal and ecological study. A total of 264 infants weighing less than 1000 g out of a total of 56 024 births during the study period. Different specific perinatal mortality rates by weight were calculated. The Spearman's Rho correlation coefficient was applied to assess the relationship between mortality rates and years of study, and ANOVA and Mann-Whitney test were used to compare five-year periods and tenyear periods, respectively. Results. There were 131 perinatal deaths, 82 stillbirths and 49 early neonatal deaths; 64.1% of them occurred before 27 weeks of gestation. Only the fetal mortality rate was statistically significant, although perinatal mortality showed a downward trend, without reaching significance. The main immediate causes of death were extreme prematurity, intrauterine hypoxia and infection. The underlying causes related to death in this group of newborn infants were infection caused by premature rupture of membranes, maternal hypertension, uncontrollable preterm labor and twin pregnancy. Conclusions. The reduction in mortality rates in this group of newborn infants is undergoing a slowdown.