Does the urban environment cause psychosis?

The paper by Sundquist et al is a welcome addition to a growing body of evidence linking exposures in the urban environment to the onset of schizophrenia (Sundquist et al , 2004, this issue). They also report, in agreement with the literature, that a similar association exists for depression of severity requiring hospital admission, albeit of a much lower effect size than that for schizophrenia and with the caveat that only in a small and biased proportion of cases is the person with clinical depression ever admitted to hospital. The paper represents a truly prospective analysis, and also considers confounding by other important demographic variables and changing exposure status over the period of observation.