The branching ratio for the leptonic decay of charged B mesons (B- → tau (-)[([nu])over bar](tau)) has been measured using selected leptonic tau (-) → l(-)nu (tau)[([nu])over bar](l) and hadronic tau (-) → nu X-tau decays in Z → b (b) over bar decays recorded by DELPHI at LEP1 in 1992-1995. The result, BR(B- → tau (-)[([nu])over bar](tau)) lt 1.1 x 10(-3) at the 90% confidence level, is consistent with standard model expectations and puts a constraint on the ratio tan [beta]/MH+/- lt 0.46 (GeV/c(2))(-1) in the framework of models with two Higgs doublets (type II Higgs doublet model). From the missing energy distribution in Z → b (b) over bar decays without identified leptons, the b → tau[([nu])over bar]X-tau branching ratio has been measured in the hadronic channel tau - → nu X-tau'. The result, BR(b → tau[([nu])over bar]X-tau) = (2.19 +/- 0.24 (stat) +/- 0.39 (syst))%, is consistent with the Standard Model prediction and with previous experimental measurements.