Data were obtained from the literature on the annual pattern of manic‐depressive attacks and on the time of admission to psychiatric hospitals. These data were correlated with the contemporaneous geomagnetic activity, using the Spearman rank correlation coefficient. The magnetic indices Ap, aa and Na were used, indices which are sensitive to solar corpuscular radiation. Manic‐depressive attacks and geomagnetic disturbances exhibited prominent seminannual patterns, with the correlations positive and statistically significant in half the tests. No significant outcomes were obtained with the admission data. The literature on geomagnetic effects on melatonin and on a melatonin dysfunction in depression is briefly reviewed, and a possible geomagnetic factor in depression is hypothesized.