This study aimed to examine saliva flow rates and prevalence of dental and periodontal diseases of patients with newly diagnosed severe haematological diseases and compare these findings with age-matched controls of normal population. A total of 149 patients diagnosed with haematological diseases aimed to be treated with haematological stem cell transplantation between 2008 and 2018 and 154 controls were included in the study. A dental examination was performed for patients within a maximum of 6months after diagnosis. Differences were compared in terms of the stimulated salivary flow rate (SSFR); decayed, missing and filled teeth (DMFT) index; number of teeth; caries prevalence; presence of periodontitis and acute infections. The mean SSFR of the patient group was significantly lower (1.1ml/min ± 0.7ml/min) than the mean SSFR of the controls (1.3ml/min ± 0.5ml/min; p = 0.004). The number of caries lesions was significantly higher in the patient group (mean ± SD, 1.1 ± 1.9) than in the control group (mean ± SD, 0.4 ± 1.2; p < 0.001). There were fewer teeth and a higher DMFT index in the patient group compared to the control group, but the differences were not significant. Acute symptomatic infections were observed in eight (5.4%) patients and in none of the controls (p < 0.01). Oral examinations in patients with newly diagnosed severe haematological disease demonstrated a higher prevalence of caries, acute infections and lower mean SSFR compared with the controls. These findings support the recommendations for early dental examination at the time of diagnosis.