Infection is a fatal complication in cancer patients that sometimes is not distinguished from tumour progression. We compared the diagnostic value of procalcitonin (PCT), C-reactive protein (CRP) and lactate dehydrogenase (LDH) in paediatric malignant solid tumour concurrent with infection and tumour progression. The 152 children enrolled were divided into infection and control groups. Each group was divided further into stable and progression groups. An intergroup comparison was made in terms of serum PCT, CRP and LDH in all children. PCT, CRP and LDH levels were significantly higher in the infection than in the control groups (P < 0.05). Among the controls, PCT, CRP and LDH levels were significantly higher in the progression than in the stable groups (P < 0.05). In diagnosing infection, the sensitivity and specificity of PCT and CRP at the cutoff values of 0.296 ng/mL and 28.13 mg/L were relatively better than those at 0.5 ng/mL and 10 mg/L, respectively. LDH had the highest correlation with tumour progression, whereas PCT had the lowest (LDH, r = 0.684; CRP, r = 0.570; PCT, r = 0.322). Thus, PCT has the highest value in diagnosing infection and is less susceptible to tumour progression than CRP. LDH has obvious advantages in judging tumour progression.