This paper is based on laboratory observations of the millipede Pseudopolydesmus pinetorum and gives general information about its natural history with a focus on reproduction and growth. In general, eggs were laid in the spring and adults died in the summer. A given female laid eggs several times before death in batches of about 70–300, which were enclosed in igloo-like chambers constructed of fecal material. The fecal material was formed into flat shingles within the everted rectum and used to build the chamber walls. Chambers had no ventilation openings, but were topped with a chimney-like structure of uncertain function and finally covered with additional fecal material and a layer of debris. Hatchlings exited their chamber in about 10 to 20 days, depending on temperature, and began to feed. They moved about as a flock (first instars only) and if another flock was present, the flocks united. Molting occurred in molting chambers; earlier instars usually made theirs in the soil, but later instars often made igloo-like chambers on the surface that were comparable to egg chambers. Later instars spent about 10 days in the chamber. Most juveniles overwintered in their sixth or seventh stadium and new adults emerged and mated in the spring. Adults of uncertain age collected in October did not lay eggs until late January. If they were prodded, the first few instars produced a drop of secretion, assumed to be defensive, from their anuses and a pair of lateral paranotal pores; these instars tended to hunker down and hold their positions, but later instars simply fled.