A method of selecting one or more patient-specific clonotypes correlated with a lymphoid neoplasm for monitoring a minimal residual disease thereof, the method comprising the steps of: (a) amplifying molecules of nucleic acid from T-cells and/or B-cells of a sample obtained from a patient, the molecules of nucleic acid comprising recombined DNA sequences from T-cell receptor genes or immunoglobulin genes; (b) sequencing the amplified molecules of nucleic acid to form a clonotype profile; (c) comparing clonotypes from the clonotype profile to clonotypes of a clonotype database, wherein the clonotype database comprises clonotypes of clonotype profiles of at least 10 4 clonotypes from at least 10 individuals other than the patient, to determine a presence, absence and/or level in the clonotype database of each clonotype from the clonotype profile, wherein the step of comparing includes counting a clonotype as present in the clonotype database if a clonotype in the clonotype database is a member of the same clan as the clonotype of the clonotype profile, and a clonotype is considered to be a member of the same clan if (i) the clonotype of the clonotype database is at least ninety percent identical to the clonotype of the clonotype profile; (ii) the clonotype of the clonotype database and the clonotype of the clonotype profile each comprise recombined sequences from immunoglobulin heavy chain and are related by a VH replacement; (iii) the clonotype of the clonotype database and the clonotype of the clonotype profile have identically mutated V region and J region but have a different NDN region; (iv) the clonotype of the clonotype database and the clonotype of the clonotype profile each comprise recombined sequences from immunoglobulin heavy chain and are related by hypermutation; or (v) if the clonotypes have undergone one or more insertions and/or deletions of from 1-10 bases; and (d) selecting the one or more patient-specific clonotypes for monitoring the minimal residual disease which are each correlated with the lymphoid neoplasm and which are each: i) absent from the clonotype database; or ii) at a level in the clonotype database below a predetermined frequency. (a) amplifying molecules of nucleic acid from T-cells and/or B-cells of a sample obtained from a patient, the molecules of nucleic acid comprising recombined DNA sequences from T-cell receptor genes or immunoglobulin genes; (b) sequencing the amplified molecules of nucleic acid to form a clonotype profile; (c) comparing clonotypes from the clonotype profile to clonotypes of a clonotype database, wherein the clonotype database comprises clonotypes of clonotype profiles of at least 10 4 clonotypes from at least 10 individuals other than the patient, to determine a presence, absence and/or level in the clonotype database of each clonotype from the clonotype profile, wherein the step of comparing includes counting a clonotype as present in the clonotype database if a clonotype in the clonotype database is a member of the same clan as the clonotype of the clonotype profile, and a clonotype is considered to be a member of the same clan if (i) the clonotype of the clonotype database is at least ninety percent identical to the clonotype of the clonotype profile; (ii) the clonotype of the clonotype database and the clonotype of the clonotype profile each comprise recombined sequences from immunoglobulin heavy chain and are related by a VH replacement; (iii) the clonotype of the clonotype database and the clonotype of the clonotype profile have identically mutated V region and J region but have a different NDN region; (iv) the clonotype of the clonotype database and the clonotype of the clonotype profile each comprise recombined sequences from immunoglobulin heavy chain and are related by hypermutation; or (v) if the clonotypes have undergone one or more insertions and/or deletions of from 1-10 bases; and (i) the clonotype of the clonotype database is at least ninety percent identical to the clonotype of the clonotype profile; (ii) the clonotype of the clonotype database and the clonotype of the clonotype profile each comprise recombined sequences from immunoglobulin heavy chain and are related by a VH replacement; (iii) the clonotype of the clonotype database and the clonotype of the clonotype profile have identically mutated V region and J region but have a different NDN region; (iv) the clonotype of the clonotype database and the clonotype of the clonotype profile each comprise recombined sequences from immunoglobulin heavy chain and are related by hypermutation; or (v) if the clonotypes have undergone one or more insertions and/or deletions of from 1-10 bases; and (d) selecting the one or more patient-specific clonotypes for monitoring the minimal residual disease which are each correlated with the lymphoid neoplasm and which are each: i) absent from the clonotype database; or ii) at a level in the clonotype database below a predetermined frequency. i) absent from the clonotype database; or ii) at a level in the clonotype database below a predetermined frequency.