The signal encoded by a sensory neuron is usually characterized as the cell's average response to repeated presentations of a stimulus. However, each stimulus presentation elicits a slightly different response. This response variability may obscure the signal represented by neural activity, but it might also be an important aspect of a neuron's message and in some instances may even serve useful function. Here we present evidence that response variability (noise) in primate retinal ganglion cells at photopic light levels is (i) independent of the amplitude of either the stimulus or the response and is therefore additive, (ii) independent of receptive field size and retinal eccentricity, and (iii) similar for all primate ganglion cells. Our results show that the primate retina maintains a uniform noise level across the entire visual field and suggest that the noise originates within the ganglion cells themselves.