The need for a 6-min walk distance (6-MWD) reference equation for healthy North African adults older than 40 years was assessed in a prospective cross-sectional study. Anthropometric data and 6-MWD were measured in 229 healthy Tunisian adults (125 women) over 40 years old. Two subgroups of 38 women were identified according to the parity (low<or=5; high>or=6). The published reference equations did not reliably predict measured 6-MWD. The 6-MWD was significantly correlated with gender, age, weight and height (p<0.001). The combination of these parameters explained 77% of the 6-MWD variability in the equation: 6-MWD (m)=-160.27 x gender (0: men; 1: women) - 5.14 x age (yr) - 2.23 x weight (kg)+2.72 x height (cm)+720.50. Parity accelerated the 6-MWD decline (r=-0.39, p<0.05) and women distinguished only by parity (<or=5 vs. >or=6) showed different 6-MWD (589+/-60 m vs. 555+/-57 m, p<0.05). In an additional group of 30 adults prospectively studied to validate the equation, the agreement between the measured and equation-predicted 6-MWD was satisfactory. In conclusion, this reliable 6-MWD reference equation enriches the World Bank and provides an important element of interpretation for women with high parity.