Background: Leukaemia is the eleventh commonest UK cancer. The four main sub-types have different clinical profiles, particularly between chronic and acute types. Aim: To identify the symptom profiles of chronic and acute leukaemia in adults in primary care. Design and setting: Matched case-control studies using Clinical Practice Research Datalink records. Methods: Putative symptoms of leukaemia were identified in the year before diagnosis. Conditional logistic regression was used for analysis; to estimate risk, positive predictive values (PPVs) were calculated, using Bayes’ theorem Results: 4,655 cases were available aged ≥40 years, diagnosed between 2000 and 2009, with 2,877 being chronic leukaemia (CL), 937 acute leukaemia (AL) and 841 of unreported subtype, with 20,719 age, sex and practice-matched controls. The two studies examined CL and AL separately. Ten symptoms were independently associated with CL, the three strongest associations being for: lymphadenopathy, odds ratio 22 (95% confidence interval 13,36), weight loss 3.0 (2.1,4.2) and bruising 2.3 (1.6,3.2). Thirteen symptoms were independently associated with AL, the three strongest being: nosebleeds and/or bleeding gums 5.7 (3.1,10), fever 5.3 (2.7,10) and fatigue 4.4 (3.3,6.0). Infection was reported frequently in both AL and CL, but the associations were small. No individual symptom or combination of symptoms had a PPV >1%. Conclusions: The symptom profiles of CL and AL have both overlapping and distinct features. This presents a dichotomy for GPs: diagnosis, by performing a full blood count, is easy; however, the symptoms of leukaemia are non-specific and of relatively low risk. This explains why many leukaemia diagnoses are unexpected findings.