Aim: The study was aimed at assessing the difficulties in the diagnosis of the first episode of idiopathic nephrotic syndrome in children, based on the analysis of the initial presenting symptoms, laboratory findings and comorbidities, and evaluating the effect of the time to diagnosis on the course of the disease and its management. Material: The study included the clinical characteristics of 51 paediatric patients aged 4.89 ± 2.72 years. Factors such as the initial presenting symptoms/reason for performing urinalysis, time to diagnosis and presence of comorbid diseases were analysed. On hospital admission, clinical symptoms, laboratory findings and time to remission were assessed. Results: In 40 (78%) children urinalysis was prompted by the presence of oedema, in 11 (22%) by abdominal pain, recurring respiratory tract infections, or was performed as followup to infection. The time from onset of oedema to hospital admission was 1–60 days (median 5.5). Twenty-five children were admitted into hospital within 7 days from disease onset, 10 children – within 8–14 days, 5 children – after more than 14 days. Twelve patients had a recent history of allergy, 9 – frequent respiratory tract infections, 1 – urinary tract infections, and 2 had a family history of nephrotic syndrome. On hospital admission, 40 children presented with oedema (transudation of fluids in to body cavities was present in 27 patients), 25 – with infections (respiratory or gastrointestinal), 8 – with carious lesions, 3 – with insect stings. Laboratory testing showed nephrotic proteinuria – 303 ± 224 mg/kg/day, hypoalbuminemia – 2 ± 0.4 g/dL, mean total cholesterol level – 332.8 ± 104 mg/dL, triglycerides – 222.6 ± 95.3 mg/dL. Proteinuria resolved on average after 9 ± 5.75 days from treatment. A positive correlation has been demonstrated between the number of days that the symptoms persisted and total cholesterol level (r = 0.36, p = 0.012). Conclusions: In 37.5% of children, the diagnosis of idiopathic nephrotic syndrome is delayed, despite oedema. Seventy-one per cent of the children have been found to show signs of an acute or chronic inflammatory condition.