We present a first study of truncation of the stellar disks of spiral galaxies in the near infrared. Observations of NGC 4013, NGC 4217, NGC 6504 and NGC 5981 were made with the CAIN NIR camera on the CST in Tenerife. This wavelength range provides the best description of the phenomenon, not only because extinction effects are minimized, but also because the distribution of the old stellar population is directly obtained. The four galaxies are edge-on and an inversion method was developed to obtain the deprojected profiles. We did not assume any model of the different galactic components. The ``truncation curve'', i.e. T(R) = mu (R)- mu D(R), where mu is the actual surface brightness in mag/arcsec2 and mu D the exponential disk surface brightness, has been obtained with unprecedented precision. It is suggested that T(R) is proportional to (Rt-R)-1, where Rt is the truncation radius, i.e. the radius beyond which no star is observed.