Objective To summarize the imaging manifestations of 18F-FDG PET/CT in patients with secondary hemophagocytic lymphohistiocytosis (sHLH).Methods From January 2008 to June 2012,31 patients (18 males,13 females,average age:42 years) with sHLH were enrolled.All patients were divided into 3 groups:malignancy associated HLH (MAHLH) group (n =13),infection associated HLH (IAHLH) group (n =13) and rheumatosis associated HLH (RAHLH) group (n =5).They all underwent 18F-FDG PET/CT and SUVmax of lesions in each group was calculated.One-way analysis of variance and two-sample t test were used to analyze the SUVmax.Results Twenty-three patients were found splenomegaly with high FDG uptake,including 4 RAHLH patients,9 IAHLH patients and 10 MAHLH patients.The splenetic FDG uptake values (SUVmax) of RAHLH,IAHLH and MAHLH groups were 3.16±0.61,5.67±3.37 and 6.04±3.06,respectively (F=1.051,P>0.05).The SUVmax of enlarged lymph nodes in IAHLH (n=8) and MAHLH groups (n =7) was 5.35± 1.69 and 10.14±5.24,respectively (t =-2.456,P<0.05).Increased uptake in bone marrow was found in 17 patients,including 1 RAHLH patient,7 IAHLH patients and 9 MAHLH patients.The SUVmax of bone marrow in IAHLH and MAHLH patients was 5.31±2.05 and 6.36± 3.71 respectively (t=-0.670,P>0.05).There were 10 cases of hepatomegaly,but only 4 of them had intense FDG uptake (SUVmax 4.9-10.2).The SUVmax of RAHLH,IAHLH and MAHLH groups was 3.02± 1.31,5.62±2.45 and 8.15±4.38,respectively (F=9.123,t=2.562,5.236,3.030,all P<0.05).Conclusions RAHLH mostly showed splenomegaly with high FDG uptake,IAHLH and MAHLH both showed splenomegaly with lymph node and bone marrow invasion.The SUVmax of MAHLH was the highest.18F-FDG PET/CT imaging manifestations of sHLH may be helpful to improve the diagnostic accuracy. Key words: Lymphohistiocytosis, hemophagocytic ; Tomography, emission-computed; Tomography, X-ray computed ; Deoxyglucose