We present a study of the magnetoresistance of highly oriented pyrolytic graphite (HOPG) as a function of the sample size. Our results show unequivocally that the magnetoresistance reduces with the sample size even for samples of hundreds of micrometers size. This sample size effect is due the large mean free path and Fermi wavelength of carriers in graphite and may explain the observed practically absence of magnetoresistance in micrometer confined small graphene samples where quantum effects should be at hand. These were not taken into account in the literature yet and ask for a revision of experimental and theoretical work on graphite.PACS numbers: 81.05. Uw,72.80.Cw Graphitic systems are nowadays a field of intensive activity [1]. There have been observations of quantum Hall effect in HOPG [2,3] as well as very large anisotropy in the electrical conductance (ratio between current parallel to perpendicular to the graphene planes) larger than 10 4 at room temperature [1]. Graphite looks as a good conductor in plane and an insulator between planes leading to a weak screening to external electric fields [4]. This means that an external electric field penetrates by tens of nanometers in graphite, in contrast to a normal metal where the field is screened in the first atomic layers. In fact the dielectric constant of graphite at optical frequencies is positive, insulator like (ǫ plane = 5.6 + i7.0, ǫ c = 2.25) [5,6]. Electric field microscopy [7] detects that regions of graphite are more insulating than others upon the interconnections of graphite planes produced by defects and their overall density that influences the density of states and the Fermi level. The material exhibits a huge magnetic field driven metal-insulator transition [1,8]. Its band structure and interband transitions with electron and hole carriers manifest in a huge ordinary magnetoresistance (OMR) [2,9]. All these effects happen in macroscopic size samples of the order of millimeters.A large research activity has been recently started on a few graphene layers (FLG) [10] with typical size of a few microns. Strikingly, the OMR in FLG samples is practically suppressed even at T < 4 K, in contrast to bulk HOPG or Kish graphite where the OMR is 1000% at B 0.5 T at low temperatures [1]. Earlier work with graphite samples in the micrometer range showed similar behavior [11,12]. However, the question on what happens when the graphite sample size is reduced has not been correctly addressed and the experimental data may need a new interpretation. The size of the sample is very important for defining the properties of the system because the de-Broglie wavelength for massless Dirac6 m/s is the Fermi velocity and a typical Fermi energy k B E F 100 K) or for massive carriers with effective mass m ⋆ 0.01m, λ m = h/ √ 2m ⋆ E F , as well as the Fermi wavelength λ F ∼ 2πn −1/2 are of the order of microns or larger due to the low density of Dirac and massive fermions. Moreover, one can show that in such micron size systems new quantum mechanical oscillations ap...