The concept of seasonal and secular cycling of initial autoantibody plasma levels in children with diabetes mellitus 1 is not common, despite the known fluctuations in one of the triggering factors, i.e., various enteroviral infections. The aim of this study was therefore to assess the trends and cycles in the time series of IA2-autoantibody (ab) blood plasma levels measured in each patient at the moment of diagnosis of the disease, before the first injection of insulin. In a retrospective study, the IA2-ab data, with each item related to a calendar day, were analyzed from 83 male and 108 female patients aged up to 14 years, with the date of disease menifestation between January 1993 and December 1999. The data source was the Slovak National Register of Childhood Diabetes. The plasma levels of the autoantibody against pancreatic tyrosine phosphatase (IA2-ab) were measured by radioimmunoassay. The chronogram of the daily observed values, modified by moving averages, from three successive data items per patient, was processed by Halberg's cosinor method to test the presence of seven-year sinusoids and one-year rhythms. One seven-year sinusoid, peaking in February 1998 (boys) and in October 1996 (girls), and a seasonal rhythm culminating in May/June each year were significant. There are some similarities to the cycling of other variables such as the incidence of diabetes, the birth of future diabetics, Coxsackie virus epidemics and pancreatic glutamic acid decarboxylase (GAD 65) autoantibody. Moreover, some cosmo-geophysical periods also seem to be cycling in a parallel manner. The novelty of this contribution is that it examines the seasonal cycling of the autoantibody, connected with the pathogenesis of diabetes and directed against IA2-ab.