Viruses, including the respiratory syncytial virus, are the most common aetiological factor of respiratory infections in children. The disease most often occurs between November and April in the northern climate zone, with a peak incidence in January and February. A total of 90% of children up to 2 years of age become infected with respiratory syncytial virus. The virus is recognised as the most common pathogen causing bronchiolitis and pneumonia in children up to 2 years old. Respiratory syncytial virus infection is the cause of 17–20% of all infantile hospitalisations. It stimulates both humoral and cellular responses of the immune system, which involves a number of cells (neutrophils, eosinophils) and inflammatory mediators (IL-1, IL-5, IL-6, IL-11, TNF-α, MIF-1a, IL-8, RANTES). It is assumed that apart from its effects on the immune system, respiratory syncytial virus also affects the neurogenic regulation of respiratory smooth muscle tension, resulting in bronchial contraction. Respiratory syncytial virus infection leads to lymphocyte Th1/Th2 imbalance with the dominance of Th2, which can indicate a further relationship with asthma. The correlation between early respiratory syncytial virus infection and the recurrence of post-infection wheezes and asthma development later in life constitutes a subject of numerous discussions. Long-term research demonstrated a relationship between respiratory syncytial virus infections and obstructive ventilatory impairment in the first decade of life. However, no clear causal relationship was found. It is assumed that respiratory syncytial virus infection can only manifest in children with genetic predisposition to this type of response.