We have searched for B-s(0) --> hh decays, where h stands for a charged or neutral kaon, or a charged pion. These results are based on a 23: 6 fb(-1) data sample collected with the Belle detector on the Y(5S) resonance at the KEKB asymmetric-energy e(+)e(-) collider, containing 1.25 x 10(6) B-s(()*())(B) over bar (()(s)*()) events. We observe the decay B-s(0) --> K+K- and measure its branching fraction, B(B-s(0) --> K+K-) = [3.8(-0.9)(+1.0)(stat) +/- 0.5(syst) +/- 0.5(f(s))] x 10(-5). The first error is statistical, the second is systematic, and the third error is due to the uncertainty in the B-s(0) production fraction in e(+)e(-) --> b (b) over bar events. No significant signals are seen in other decay modes, and we set upper limits at the 90% confidence level: B(B-s(0) --> K- pi+) < 1.2 x 10(-5), B(B-s(0) --> pi(+)pi(-)) < 2.6 x 10(-5), and B(B-s(0) --> K-0(K) over bar (0)) < 6.6 x 10(-5).