Gait and Balance Scale (GABS) consists of historical information and examination of 14 different gait and balance parameters designed to assess the severity of these functional domains. Thirty-five patients with Parkinson's disease (PD), Hoehn and Yahr stages 1-3, were tested during their "off" period. GABS items were compared to quantitative data from two computerized gait analysis instruments, GAITRite and Pro Balance Master. Intra-class correlation coefficients were calculated to establish reliability. Intra-rater test-retest reliability was determined using Cohen's Kappa statistic. Concurrent validity was derived using the Spearman's rho test with the items from GABS, GAITRite and Balance Master. Intra-rater reliability was high with k>0.41 (k=kappa statistic) for 17 items, 6 had k>0.61. When performing validity measurements, a number of items on the GABS had a correlation coefficient significant at p<0.01 (2-tailed). Posture, pull test, balance during stance, single limb stance, tandem stance, turning, toe walking and functional reach had significant correlation with Balance Master data (R=0.46-1). Gait, arm swing, gait speed, steps/5 m, 'up-and-go test', modified performance oriented assessment of gait scale and provocative testing had significant correlation with the GAITRite items (R=0.51-0.83). GABS is an easy-to-use comprehensive clinical scale with high intra-rater and internal item reliability. We have shown concurrent validity with two computerized gait analysis instruments. We expect GABS to have a particular utility in clinical trials designed to modify functional impairment associated with abnormalities in gait and balance.