A process for producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, using a hydrocracking and hydroisomerisation catalyst comprising at least one hydro-dehydrogenating metal selected from the group formed by metals of group VIB and group VIII of the periodic table and a support comprising at least one crystallised IZM-2 solid exhibiting an X-ray diffraction pattern including at least the rays set out in the following table: 2 theta (°) dhkl (Å) Irel 2 theta (°) dhkl (Å) Irel 5.07 17.43 ff 19.01 4.66 ff 7.36 12.01 FF 19.52 4.54 ff 7.67 11.52 FF 21.29 4.17 m 8.78 10.07 F 22.44 3.96 f 10.02 8.82 ff 23.10 3.85 mf 12.13 7.29 ff 23.57 3.77 f 14.76 6.00 ff 24.65 3.61 ff 15.31 5.78 ff 26.78 3.33 f 15.62 5.67 ff 29.33 3.04 ff 16.03 5.52 ff 33.06 2.71 ff 17.60 5.03 ff 36.82 2.44 ff 18.22 4.87 ff 44.54 2.03 ff wherein FF = very strong; F = strong; m = moderate; mf = moderately weak; f = weak; ff = very weak and having a chemical composition expressed on an anhydrous basis, in terms of moles of oxides, by the following general formula: XO 2: aY 2 O 3: bM 2/n O in which X represents at least one tetravalent element, Y represents at least one trivalent element and M is at least one alkali metal and/or an alkaline earth metal of valency n, a and b respectively representing the number of moles of Y 2 O 3 and M 2/n O and a is between 0 and 0.5 and b is between 0 and 1; said crystallised IZM-2 solid being prepared by reacting an aqueous mixture referred to as a gel comprising at least one source of at least one oxide XO 2, optionally at least one source of at least one oxide Y 2 O 3, optionally at least one source of at least one alkali metal and/or alkaline earth metal of valency n, at least one organic species R comprising two quaternary nitrogen atoms, the mixture being of the following molar composition: XO 2 /Y 2 O 3: at least 2, preferably at least 20, more preferably 60 to 600, H 2 O/XO 2: 1 to 100, preferably 10 to 70, R/XO 2: 0.02 to 2, preferably 0.05 to 0.5, and M 2/n O/XO 2: 0 to 1, preferably 0.005 to 0.5; wherein X is one or more tetravalent elements selected from the group formed by the following elements: silicon, germanium, titanium, preferably silicon, wherein Y is one or more trivalent elements selected from the group formed by the following elements: aluminium, iron, boron, indium and gallium, preferably aluminium, and wherein M is one or more alkali metal and/or alkaline earth metals selected from lithium, sodium, potassium, calcium, magnesium and the mixture of at least two of said metals, preferably sodium; the gel obtained being subjected to a hydrothermal treatment under an autogenous reaction pressure at a temperature of between 120°C and 200°C until said crystallised IZM-2 solid is formed, then at the end of the hydrothermal treatment leading to crystallisation of said IZM-2 solid the solid phase is calcined by one or more heating steps performed at a temperature of between 100 and 1000°C for a period of between 3 hours and 48 hours. XO 2 /Y 2 O 3: at least 2, preferably at least 20, more preferably 60 to 600, H 2 O/XO 2: 1 to 100, preferably 10 to 70, R/XO 2: 0.02 to 2, preferably 0.05 to 0.5, and M 2/n O/XO 2: 0 to 1, preferably 0.005 to 0.5; wherein X is one or more tetravalent elements selected from the group formed by the following elements: silicon, germanium, titanium, preferably silicon, wherein Y is one or more trivalent elements selected from the group formed by the following elements: aluminium, iron, boron, indium and gallium, preferably aluminium, and wherein M is one or more alkali metal and/or alkaline earth metals selected from lithium, sodium, potassium, calcium, magnesium and the mixture of at least two of said metals, preferably sodium; the gel obtained being subjected to a hydrothermal treatment under an autogenous reaction pressure at a temperature of between 120°C and 200°C until said crystallised IZM-2 solid is formed, then at the end of the hydrothermal treatment leading to crystallisation of said IZM-2 solid the solid phase is calcined by one or more heating steps performed at a temperature of between 100 and 1000°C for a period of between 3 hours and 48 hours.