Accurate assessment of age is important for effective captive husbandry techniques and assists in understanding developmental processes, population dynamics, reproductive strategies and seasonal breeding. Using linear and non-linear regression, this study analysed the growth rate of the head and pes length of known-age, captive-born pouch young of the black-footed rock-wallaby, Petrogale lateralis 'MacDonnell Ranges race'. Growth curves for head and pes length from the captive-born pouch young were then used to predict the age of pouch young of P. lateralis pearsoni using data collected from the field. Observations on the development of the eyes, ears and body of P. lateralis 'MacDonnell Ranges race' were also recorded. Results showed that a non-linear growth model best described the head-length growth of captive-born pouch young (r2 = 99.5%), whereas logistic regression was the most accurate predictor of pes-length growth (r2 = 99.6%). No significant differences were found when the two growth models were applied to head and pes data from wild pouch young, suggesting that the growth models derived from captive animals can be used to accurately predict the age of pouch young in the wild. During a preliminary cross-fostering trial, we examined growth of the head and pes length in pouch young of P. lateralis 'MacDonnell Ranges race' that had been cross-fostered onto the teats of surrogate tammar wallaby (Macropus eugenii) mothers; comparisons were made to the growth rate of pouch young of the same race that had remained with their natural mothers.