Method for analysing microorganisms (10 i), the microorganisms being placed in a sample, the sample comprising a viability marker (10 v) that is able to modify an optical property of the microorganisms differently depending on whether they are dead or alive, the method comprising the following steps: a) illuminating the sample using a light source, the light source emitting an incident light wave that propagates towards the sample along a propagation axis; b) acquiring, using an image sensor, an image ( I 0) of the sample, which image is formed in a detection plane ( P 0), the sample being placed between the light source and the image sensor, the image being representative of an exposure light wave to which the image sensor is exposed under the effect of the illumination, the image containing interference patterns due to interference between a portion of the incident light wave transmitted by the sample and the diffraction of the incident light wave by the microorganisms; the method being characterized in that it also comprises the following steps: c) determining radial positions (x i, y i) of various microorganisms (10 i) in a plane parallel to the detection plane, each radial position being associated with one microorganism; d) to the image ( I 0) acquired in step b), applying a propagation operator (h), so as to compute at least one characteristic quantity (M, <p) of the exposure light wave, at each radial position (x i, y i) determined in step c), and at a plurality of distances (z) from the detection plane ( P 0); e) forming a profile (M i ( z), φ i ( z)) representing a variation in the characteristic quantity computed in step d) along an axis parallel to the propagation axis and passing through each radial position (x i, y i) determined in step c), each profile being associated with one microorganism (10 i); f) depending on each profile formed in step e), classifying between microorganisms that are dead and microorganisms that are alive. a) illuminating the sample using a light source, the light source emitting an incident light wave that propagates towards the sample along a propagation axis; b) acquiring, using an image sensor, an image ( I 0) of the sample, which image is formed in a detection plane ( P 0), the sample being placed between the light source and the image sensor, the image being representative of an exposure light wave to which the image sensor is exposed under the effect of the illumination, the image containing interference patterns due to interference between a portion of the incident light wave transmitted by the sample and the diffraction of the incident light wave by the microorganisms; c) determining radial positions (x i, y i) of various microorganisms (10 i) in a plane parallel to the detection plane, each radial position being associated with one microorganism; d) to the image ( I 0) acquired in step b), applying a propagation operator (h), so as to compute at least one characteristic quantity (M, <p) of the exposure light wave, at each radial position (x i, y i) determined in step c), and at a plurality of distances (z) from the detection plane ( P 0); e) forming a profile (M i ( z), φ i ( z)) representing a variation in the characteristic quantity computed in step d) along an axis parallel to the propagation axis and passing through each radial position (x i, y i) determined in step c), each profile being associated with one microorganism (10 i); f) depending on each profile formed in step e), classifying between microorganisms that are dead and microorganisms that are alive.