  We use the Hubble Ultra Deep Field (UDF) to study the galaxy luminosity-size
(M-Re) distribution. With a careful analysis of selection effects due to both
detection completeness and measurement reliability we identify bias-free
regions in the M-Re plane for a series of volume-limited samples. We also
investigate the colour-log(n) distribution of these galaxies and further
subdivide our data by structural type to separately study compact and diffuse
objects. By comparison to the nearby Millennium Galaxy Catalogue, we present
tenative evidence for evolution of diffuse, disk-like galaxies with redshift --
both in mean surface brightness and the slope of the M-Re relation. In contrast
we find no evidence of structural evolution in the compact galaxy M-Re relation
over this redshift range, although there is a suggestion of colour evolution.
We also highlight the importance of considering surface brightness dependent
measurement biases in addition to incompleteness biases. In particular, the
increasing, systematic under-estimation of Kron fluxes towards low surface
brightnesses may cause diffuse, yet luminous, systems to be mistaken for faint,
compact objects.

Astrophysics