Finland and Sweden have the highest incidence of insulin-dependent diabetes in children in the world, about 3–4 times that of countries in the Mediterranean area, with the exception of Sardinia. We have collected information from several European clinics and from Pittsburgh, USA, in order to find out whether this difference in incidence is associated with corresponding differences of the disease pattern. Patients in Finland or Sweden (North) and Pittsburgh were younger (<10 years="" old)="" at="" diagnosis="" compared="" with="" those="" in="" the="" other="" clinics="" in="" europe="">P<0.05>P<0.02). in="" the="" north,="" boys="" were="" in="" excess="" (58%)="" in="" contrast="" to="" france="" (40%)="" and="" pittsburgh="" (46%).="" patients="" in="" the="" north="" had="" a="" shorter="" duration="" of="" symptoms=""><8>P<0.001) and="" higher="" blood="" glucose="" (="">20 mmol/l;P<0.05) than="" those="" attending="" the="" other="" european="" clinics.="" irrespective="" of="" age,="" there="" were="" more="" ica-positive="" patients="" in="" the="" north="" (94%)="" than="" in="" berlin-vienna="">P<0.01) or="" in="" france="">P<0.01). there="" was="" a="" tendency="" for="" non-diabetic="" parents="" and="" siblings="" in="" the="" north="" to="" have="" lower="" c-peptide="" values=""><0.26 pmol/ml)="" at="" the="" time="" of="" diagnosis="" of="" the="" proband="" and="" to="" be="" ica-positive="" more="" often="" than="" relatives="" in="" the="" other="" european="" clinics.="" the="" seasonal="" variation="" of="" diagnosis,="" showed="" no="" obvious="" geographical="" differences,="" with="" recorded="" diagnosis="" always="" lowest="" during="" the="" summer.="" we="" conclude="" that="" certain="" factors="" seem="" to="" cause="" not="" only="" a="" high="" incidence="" of="" diabetes="" in="" children="" in="" finland="" and="" sweden="" but="" perhaps="" also="" a="" more="" aggressive="" early="" disease="">