The Thy-1.2 expression cassette described in this report drives strong constitutive expression of transgenes specifically in the neurons of adult transgenic mice. Transgene expression begins at P6-10, at a time when it can affect activity-dependent rearrangements of synaptic connections and neuron-glia interactions during the late phases of nervous system development. Slightly earlier expression is detected in the developing cerebellum, where transgenes could also affect granule cell migration. Probably due to the strong genetic context sensitivity of the expression construct, expression patterns differ considerably among transgenic lines. Accordingly, neuron types can be subdivided into a group that consistently displays substantial expression in all tested transgenic lines, and in those where expression is founder-specific. About a fifth of the transgenic lines displayed quite generalized expression in neurons. These properties of the Thy-1.2 expression cassette can be exploited to study the effects of transgenes during late nervous system development and in the adult, with the added opportunity of analyzing different combinations of expressing and non-expressing neurons in transgenic animals derived from different founder lines.