Proteus anguinus is an aseasonal breeder. During times of breeding, males become territorial and physically defend their territories. The qualities of an ideal territory are unknown. Once a mating territory is established by the male, he waits for females. Eventually a female will approach a male within his territory and courtship begins. It is unclear whether males and/or females release pheromones to communicate with each other. A male may potentially mate with multiple females, but a female mates with just one male.

The courtship process is distinctive. A female approaches a male, and he fans his tail towards her head. The male then touches the female's cloaca with his snout, and she reciprocates. The male walks in front of the female and deposits a spermatophore, which the female immediately picks up with her cloaca and stores in a special structure called a spermathecae.

Mating System: polygynous

Proteus anguinus breeds every 12 years, on average. The female begins laying her fertilized eggs 2 to 3 days after courtship, and may continue to lay eggs for up to 25 days. Before laying her eggs, the female establishes an egg-laying territory away from the male's territory. Clutch size averages 35 eggs. Eggs incubate for two to six months, hatching into juveniles that develop directly into adults. Olms become sexually mature at 14 to 15 years old.

Breeding interval: Proteus anguinus breeds every 12 years, on average.

Breeding season: The breeding season for Proteus anguinus is unknown.

Range number of offspring: 70 (high) .

Average number of offspring: 35.

Range time to hatching: 2 to 6 months.

Range age at sexual or reproductive maturity (female): 14 to 15 years.

Range age at sexual or reproductive maturity (male): 14 to 15 years.

Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous

A female olm guards her eggs while they incubate (2 to 6 months). She does not provide food or protection once the eggs are hatched. Males exhibit no parental investment beyond the initial sperm.

Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female)