Objective: To correlate the respiratory muscle strength and functional capacity in patients with CF. Method: Cross-sectional study in adults with cystic fibrosis. Sampling data were cataloged in Microsoft Office Excel 2007 and the variables analyzed by SPSS version 20.0 using the Student t test and the Spearman coefficient. The level of significance adopted was p < 0.05. Results: We assessed 35 patients with cystic fibrosis (44.6 ± 19.0 years), the great majority of patients in FC (n=22) did not present weakness of the inspiratory muscles (MIP-90,7 ± 27.4 cmH2O). It was not found statistically significant differences only between the adult and elderly patients. There was a positive correlation between MIP and MEP and a six-minute walk test (6MWT) in participants with respiratory muscle weakness and in the elderly. There was statistically significant difference between the averages of the distance covered on the 6MWT and the maximal respiratory pressures with the average of what was envisaged for these variables. Conclusion: All groups presented limitation of respiratory strength and functional capacity. The correlations between the respiratory pressures with the 6MWT were low and small in adults and individuals without respiratory muscle weakness; moderate to high in the elderly; small to moderate in women; small and negative in men; and high in patients with respiratory muscle weakness.