The purpose of this study was to examine changes in physical activity and fitness variables in members of 8 volunteer families after 3 months of home use of the Wii Fit™ interactive video game. Pre and postintervention measurements were obtained from 21 subjects relative to physical activity (5 days of accelerometry), aerobic fitness (graded treadmill test), muscular fitness (push-ups), flexibility (sit-and-reach test), balance (composite equilibrium score), and body composition (body mass index and % body fat). Use characteristics of the Wii Fit™ device were also determined. A series of 2 (age group) × 2 (time) repeated measures analyses of variance were conducted to assess changes over time and between adults and children. Three months of home Wii Fit™ use revealed no significant age group × time interactions or main effects of group or time for daily physical activity, muscular fitness, flexibility, balance, or body composition. An age group × time interaction (p = 0.04) was observed in peak VO2 (ml·kg(-1)·min(-1)) with children displaying a significant (p = 0.03) increase after 3 months of Wii Fit™ use, whereas adults showed no significant (p = 0.50) change. Daily Wii Fit™ use per household declined by 82% (p < 0.01) from 21.5 ± 9.0 min·d(-1) during the first 6 weeks to 3.9 ± 4.0 min·d(-1) during the second 6 weeks. Most measures of health-related fitness in this exploratory study remained unchanged after 3 months of home use of the popular Wii Fit™ whole-body movement interactive video game. Modest daily Wii Fit™ use may have provided insufficient stimulus for fitness changes.