An elaborate courtship takes place involving extensive vocalization, a comical sort of dance, and the male showering the female with urine. The testes of male porcupines descend into scrotal pouches during late August and early September. Spermatogenesis reaches its highest level during October. After mating, the female repels the male and a copulation plug is formed. The gestation period lasts between 205 and 217 days with the young being born from April to June.
Offspring are precocial with open eyes when born.
Senses of smell and hearing develop as the young grow. The quills of young porcupines are soft at birth but harden within one hour. Mothers remain with their young for up to six months. During winter months, the animals seek refuge in caves, decaying logs, or hollow trees. They do not build nests.