A pregnant and lactating adult female pygmy sperm whale (Kogia breviceps) was recovered from Moclips, Washington on November 11, 2005. Three weeks after the adult was discovered, a partially scavenged Kogia calf (standard length 1.65 m) was found approximately 70 km from the stranding site of the female. Based on the stranding circumstances (proximity of strandings, life history information), infrequency in both documented historical strandings and live sightings of Kogia in Washington, it was assumed that this was a mother/calf stranding event. Genetic tests will confirm this assumption. Comprehensive post-mortem gross examinations were performed. The female was actively lactating and was pregnant. The uterus was distended with approximately 27 L of clear serous pale yellow fluid and within the left uterine horn, was the mid gestational anatomically normal female fetus (standard length 18.5cm, weight 195g). The accumulation of fluid within the amnion is consistent with hydramnios (hydrops of the amnion) and it is difficult to resolve the contribution of this process to the loss of the dam. This condition has been documented in humans and domestic livestock and has been associated with fetomaternal or placental abnormalities, such as fetal anemia or blood incompatibility, maternal diabetes, plant toxins, infectious pathogens and twins or multiple births. The stranded calf, associated with the female that was actively lactating, is evidence that the female had at least one successful pregnancy resulting in a viable offspring. This is thought to be the first reported case of hydramnios in cetaceans and specifically a pygmy sperm whale. In this species, this condition is considered spontaneous and of limited implication for remaining populations members.