A search for doubly-charmed B decays with both charmed mesons reconstr
ucted is performed, using about 3.8 million hadronic Z decays recorded
with the ALEPH detector at LEP. A clear signal is observed in the cha
nnels B --> D-s(D) over bar(X) and B --> D (D) over bar(X) (where D ca
n be either a D-O, a D+ or a D(+)), providing the first direct eviden
ce for doubly-charmed B decays involving no D-s production. Evidence f
or associated K-S(O) and K+/- production in the decays B --> D (D) ove
r bar(X) is also presented and some candidates for completely reconstr
ucted decays B --> D-s(D) over bar(n pi), B --> D (D) over bar K-S(O)
and B --> D (D) over bar K+/- are observed. Furthermore, candidates fo
r the two-body Cabibbo suppressed decays B-O --> DD-*(+) and B- --> (
DO)-O-()D-(*-) are also observed. Measurements of the corresponding b
ranching fractions are extracted.