Severe mortalities due to luminescent vibrios occurred in pond-cultured Penaeus monodon juveniles particularly in the first 45 days of culture. Luminescent vibriosis epizootics led to reduced shrimp production due to mortalities and slow growth of affected stocks. Monitoring of bacterial population in the rearing water of several ponds was conducted from the time the ponds were flooded with water until 60 days of culture to understand the course of infection. Results showed that the occurrence of mortalities was preceded by a shift of the bacterial profile of the rearing water in infected ponds, notably the dominance of luminescent vibrios. Comparison of bacterial load in the rearing water and water source (river or open sea) showed elevated luminescent Vibrio counts in the former at 12 days to 3 weeks after initial entry of water. Histopathology of affected shrimps showed the hepatopancreas as the target organ of infection where severe inflammatory responses in the intertubular sinuses were seen.