To check whether the presence or not of free intervals between episodes could help differentiate subtypes of bipolar disorder, as suggested by the seminal controversy between Falret and Baillarger.

From 1090 bipolar I patients included in a French national study, 981 could be classified as with or without free intervals and assessed for demographic and illness characteristics.

Compared with patients with free intervals (n = 722), those without (n = 259) had an earlier age at onset, more episodes, suicide attempts, cyclothymic and irritable temperaments. The following independent variables were associated with no free intervals: being single or divorced, delay to mood stabilizer treatment, multiple hospitalizations, incongruent psychotic features, panic and generalized anxiety disorder.

“Folie à double forme” (without free intervals) and “folie circulaire” (with free intervals) may actually refer to early and later onset bipolar subtypes, insofar as most differences we found between them were previously evidenced between the latter two. We cannot, however, exclude that they might simply be two separate subtypes, whose main characteristics could be accounted for by different explanatory factors.