The aims of this study were to assess the prevalence of ketosis in type 1 diabetic patients with casual hyperglycemia (>250 mg/dl), to establish the relationship between glycemia and ketonemia during daily life, and to determine the utility of ketonemia. Capillary glycemia levels from 562 type 1 diabetic patients were recorded. Prevalence of casual hyperglycemia was 27.58%, and prevalence of asymptomatic ketonemia was 8.39%. Regarding blood ketone levels, 110 out of 155 patients (70.96%) had blood ketone levels of between 0 and 0.1 mmol/l and 32 out of 155 patients (20.63%) had blood ketone levels of between 0.2 and 0.4 mmol/l. Surprisingly, the mean glycemia levels in these subgroups did not differ and was consistently high (around 300 mg/dl), leading to the observation that even ketone levels considered as non-pathologic should probably be taken into account for a proper diabetes control. Some discrepancies between quantitative determination of ketonuria and qualitative determination of ketonemia were observed. That is in 20 patients with positive ketonuria, ketonemia was not detected, probably because ketosis was already resolved. Asymptomatic ketosis was observed in the hyperglycemic type 1 diabetic population, and metabolic control of these patients with a point of care device is recommended, together with a subsequent revision of insulin treatment. Furthermore, this study supports the opinion that the presence of ketosis, detected by beta-OHB levels, even below levels considered as pathologic, together with hyperglycemia, must be taken into account for proper monitoring and therapeutic control of diabetic patients.