One hundred and three laboratory colonies of the eastern subterranean termite. Reticulitermes flavipes (Kollar). ranging from 4 mo to 9 yr of age, were destructively sampled, and the numbers of eggs and other life stages were counted. Polygyny was maintained in 9.7% (n = 31) of the groups censused at four months, whereas monogyny was the only condition found thereafter. Polyandry was recorded in 17% of colonies sampled over a 2-yr period. Colonies set up with multiple males/females achieved similar rates of progeny (numbers, caste proportions, and biomass) compared with colonies initiated by a single royal pair. The soldier caste was present at the 4-mo census, whereas nymphs and neotenics first occurred in 2-yr-old groups. Primary queens reached a mean body mass of 7.06 mg (SD 2.4) after 2 yr and did not gain considerable weight between 2 and 4 yr. Two 6-yr-old queens weighed 17 and 18 mg, respectively, and produced the highest number of eggs per day. A simple computer model of colony growth, using both egg-laying rates obtained from our census and hypothetical egg-laying rates, revealed that the expected number of larvae matched the numbers censused in colonies up to 2 yr of age, although worker numbers were consistently overestimated. The data indicate that a monogyne colony of R. flavipes could not attain the population size occasionally described in field studies. Extrapolating laboratory data and potential reproductive mechanisms that can account for field data are discussed.