We present a practical approach for the assessment of old-growth status that is consistent with stand development theory, namely that a true old-growth stage is achieved when internal stand regeneration processes have led to the replacement of individuals recruited immediately after the last stand-initiating disturbance. Age and basal area of all individual trees and a number of stand structural attributes were evaluated for 14 stands, ranging in age from 124 to 343 years since the last stand-replacing wildfire, in the Sub-Boreal Spruce biogeoclimatic zone of north-central British Columbia. Stands were ranked on a stand development continuum of 'mature' to 'old-growth' using age-class distributions, principal components analysis of easily measured stand attributes, and ratios of replacement cohort basal area to initial cohort basal area. The latter - the ratio of the basal area of individuals recruited under the canopy to the basal area of individuals recruited immediately following disturbance - is most consistent with the conceptual definition of old growth and can serve as a quantitative measure of old-growth status. A cohort basal area ratio of 0.045 to 0.235 denotes the beginning of functional old-growth status in these forests, that is, transitional old-growth sensu Oliver (1981, Oliver and Larsen 1990). Thresholds are identified for five easily measured stand attributes that separate clearly mature from clearly old-growth stands. An old-growth scoring system is presented, based on the ratio of observed levels of those attributes to the identified thresholds, multiplied by a weighting factor derived from the correlation of each attribute with the cohort basal area ratio, which is more difficult to measure. When summed over all five attributes, an old-growth score > 1.0 denotes stands in this forest type that are functionally old growth.