The accurate measurement of health-related physical activity (PA), often interpreted as either 150 min/week of at least moderate-intensity PA (U.S. Department of Health and Human Services, 2008) or at least 30 min of at least moderate-intensity PA on 5 or more days per week (Australian Government Department of Health and Ageing [AGDHA], 2005; Haskell et al., 2007), is critical for determining current PA levels and monitoring compliance with PA guidelines (Bauman, Phongsavan, Schoeppe, & Owen, 2006). Measurement instruments need to be valid, reliable, and practical (Sallis & Saelens, 2000). It has been noted that, to evaluate total PA levels, it is necessary to include indicators of intensity, duration, frequency, energy expenditure, and activity type (Bauman et al., 2006). These more comprehensive PA measures, which often assess activity in various domains, give a detailed assessment of people's activity levels (see e.g., Craig et al., 2003; International Physical Activity Questionnaire, 2005). However, it may not be feasible to use these instruments when there are time constraints and/or limitations on research resources. Single-item PA measures, which have been examined against longer self-report measures of PA for evidence of validity, have been suggested as an alternative way to gather information about PA (Milton, Bull, & Bauman, 2010). The main aim of this study was to provide validity evidence for a single-item PA measure tailored to current PA guidelines (AGDHA, 2005; Haskell et al., 2007) against two additional PA measures: (a) a 7-day PA recall and (b) an objective PA measurement (i.e., pedometer steps). Additionally, the authors used 7-day PA recall to examine the type or intensity level the single item most relates to and determine the ability of three PA measures to detect differences between subgroups of their target population. Participants were 458 parents (n = 252 mothers, n = 206 fathers) living in Australia, predominately in Queensland (91%), with at least one child under 5 years of age. The authors found support for the scant research suggesting parents are at risk for inactivity. Specifically, parents on average engage in only 3 days/week of at least moderate-intensity PA of at least 30 min and only accumulate a 100-min median of Health Enhancing PA (HEPA). These figures fall far short of current PA recommendations. The authors also provided some evidence for the concurrent validity of the single-item PA measure, which was tailored to current guidelines. This brief PA tool may be useful for examining the PA behaviour of parents who are busy and time-pressed. (Contains 3 tables.)