An aerodynamic lens system with efficient transmission of particles in the 10-300 nm size range is used to study the efficiency of nanoparticle detection by laser ablation mass spectrometry with 193 nm and 266 nm radiation. Ideally, all particles in the beam path when the laser fires should be detected. However, the probability of particle detection is much less than 1 and dependent upon the particle type, defined by particle size and chemical composition, and the ablation conditions, defined by the laser wavelength and irradiance. Particles above 100 nm can be ablated and detected with near unit efficiency. Below 100 nm, the detection probability decreases with decreasing particle size and salt particles (sodium chloride, potassium chloride) are detected with higher efficiency than organic particles (oleic acid, 3-nitrobenzyl alcohol). The results are discussed in relation to the mechanism of laser ablation and the instrumental requirements for particle detection.