We demonstrate the detection of a molecular beam by means of a micromechanical momentum transfer detector operated in vibrational resonance. With a sensitive surface area of 0.5x0.3 mm(2) the small paddle allows us to detect a beam with 6.5x10(7) He atoms hitting the surface per second. The detector response time equals the damping time of the paddle oscillation of about 1 s. The detector is sensitive enough to measure intensities in molecular beam scattering experiments. The novel detection scheme has the potential to allow the development of a position sensitive molecular beam detector. (C) 1999 American Institute of Physics. [S0034-6748(99)01709-8].