BACKGROUND AND OBJECTIVE: Ground glass nodules (GGNs) are frequently encountered in the lungs. We report the natural history and characteristics of multiple GGNs, and propose a management plan for patients with multiple GGNs. METHODS: We retrospectively analysed patients with GGNs that met the following criteria: (i) GGN diameter of 3 cm or less, (ii) ground glass opacity proportion of 50% or more and (iii) observation without treatment for ≥6 months. We evaluated size changes in computed tomography images. Two end points, 'incidence of growth at 36 months' and 'time to growth' were analysed using logistic regression models and Cox proportional hazards model. RESULTS: Between April 2008 and December 2014, 187 patients fulfilled the inclusion criteria (78 (42%) had multiple lesions). Among the multiple-GGN patients, the median observation period was 45.5 months, 25 patients (32%) experienced GGN progression at 36 months and 4 patients (5.1%) after 36 months. Between the multiple and single GGNs, there were no significant differences in growth incidence at 36 months (P = 0.1), after 36 months (P = 0.6) or in time to growth (P = 0.3). Among patients with multiple GGNs who experienced one GGN growth, 41% of patients experienced residual GGN growth afterwards. CONCLUSION: Patients with multiple GGNs showed a tendency to growth within the first 36 months, and a significant proportion of patients experienced multiple GGN progression. We suggest that the optimal observation period for patients with multiple GGNs is 36 months, but careful observation is needed after a lesion begins to grow.